UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Clockworks, hot pots, heat machines, and chemical machines : the contrivance aspect of the machine… Bromberg, Paul 1991

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1991_A8 B75.pdf [ 7.85MB ]
Metadata
JSON: 831-1.0076839.json
JSON-LD: 831-1.0076839-ld.json
RDF/XML (Pretty): 831-1.0076839-rdf.xml
RDF/JSON: 831-1.0076839-rdf.json
Turtle: 831-1.0076839-turtle.txt
N-Triples: 831-1.0076839-rdf-ntriples.txt
Original Record: 831-1.0076839-source.json
Full Text
831-1.0076839-fulltext.txt
Citation
831-1.0076839.ris

Full Text

CLOCKWORKS, HOT POTS, HEAT MACHINES AND CHEMICAL MACHINES THE CONTRIVANCE ASPECT OF THE MACHINE METAPHOR by PAUL BROMBERG B. Sc., U n i v e r s i d a d N a c i o n a l de Colombia (Bogota), 1976 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n THE FACULTY OF GRADUATE STUDIES I n t e r d i s c i p l i n a r y Studies ( H i s t o r y and Philo s o p h y of S c i e n c e / P h y s i c s / B i o l o g y ) We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA June 1991 (c)Paul Bromberg, 1991 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada DE-6 (2/88) I i ABSTRACT From a general discussion concerning the shortcomings of the received view of s c i e n t i f i c theories and s c i e n t i f i c explanation I conclude that metaphorical thinking, u n t i l quite recently r e s t r i c t e d to l i t e r a r y analysis, may play a s i g n i f i c a n t role not only in the way theories are conceived, but also in the way that meaning is ascribed to the concepts used in science. The analysis of the l i t e r a l realm of 'machine' considers three aspects that could appear in the metaphorical assimilation of organisms to machines: the contrivance aspect, which i s the 'hardware'; the fact that machines exhibit purpose; f i n a l l y , the integrated aspect of the machine ( i t s harmony). The study i s devoted only to the f i r s t aspect. I offer a narrative of p i v o t a l ideas about the workings of the b i o l o g i c a l i n d i v i d u a l , from the clockworks of the early mechanicists to modern biochemistry, not just as a succession of discoveries but also as alleged accomplishments of the 'machine metaphor' revealing i t s scope. Some recognized milestones in the history of ideas about the inner workings of organisms are surveyed: the proposals of the early mechanicists during the S c i e n t i f i c Revolution, Lavoisier's view of res p i r a t i o n as combustion, Liebig's description of the human body as a chemical machine and the suggestion that the chemical accomplishments in l i v i n g beings are the result of myriads of fermentation-like processes. I devote special attention to the problem of the d i r e c t conversion of chemical energy into mechanical energy using the evolution of ideas about muscular contraction as the main example. During the period 1900-1930 the study of c o l l o i d a l behavior was considered to be the right path for unraveling most of the mysteries of v i t a l processes. I c a r e f u l l y describe t h i s work p a r t i c u l a r l y the proposed models for muscular contraction and enzymatic action. The dismissal of th i s c o l l o i d a l approach after the acceptance of the existence of those pa r t i c u l a r kinds of macromolecules that exist in l i v i n g organisms marks the entrance of our modern approach. One of the remarkable features of the modern approach i s the incessant elaboration of the idea of 'molecular machine'. I conclude with a discussion of the problem how l i t e r a l l y can th i s metaphor be taken? iv TABLE OF CONTENTS ABSTRACT i i LIST OF FIGURES v i ACKNOWLEDGEMENTS v i i INTRODUCTION v i i i 1. ON METAPHOR 1 1.1 INTRODUCTION 1 1.2 THE LITERAL AND THE METAPHORICAL 4 1.3 THE RECEIVED VIEW OF SCIENTIFIC THEORIES AND EXPLANATION 7 1.4 MODELS IN THE RECEIVED VIEW 12 1.5 MODELS, METAPHORS AND PARADIGMS 17 2. FROM CLOCKWORKS TO CHEMICAL MACHINES 31 2.1 INTRODUCTION 31 2.2 MECHANISM, OR MACHINISM? 33 2.3 MACHINES 4 6 V 2.3 HOT POTS, HEAT MACHINES AND CHEMICAL MACHINES . . . 55 2.3.1 LAVOISIER AND LIEBIG: THE HOT POT 56 2.3.2 HEAT MACHINES, HOT SPOTS AND CHEMICAL MACHINES 65 2.4 DISCUSSION OF THE CHEMICAL MACHINE 81 3. THE CATALYTIC MACHINES 91 3.1 NON-FERMENTATIVE FERMENTS 91 3.2 COLLOIDAL MACHINERY 103 3.2.1 WILLIAM B. HARDY 107 3.2.2 THOMAS GRAHAM AND THE ORIGINS OF COLLOIDOLOGY 112 3.2.3 FROM THOMAS GRAHAM TO WOLFGANG OSTWALD . . . 115 3.2.4 PROMISES OF COLLOIDS IN PHYSIOLOGY 123 3.2.5 BIOCHEMISTRY AND COLLOIDS 130 3.2.6 ENZYMES AS COLLOIDAL CATALYSTS 135 3.2.7 THE FADING OF BIOCOLLOIDOLOGY 140 3.3 THE AGE OF COLLOIDOLOGY 147 4. MOLECULAR MACHINERY 154 5. EPILOGUE 173 BIBLIOGRAPHY 175 v i LIST OF FIGURES Figure 1: Structure of the Sarcomere 85 Figure 2: 'Powerstroke 1 in Muscle Contraction 85 Figure 3: Fatty Acid Synthetase Complex 156 Figure 4: Picture of a Transduction Process 164 v i i ACKNOWLEDGEMENTS I am indebted to Drs. Jack Maze and Jess Brewer, who along with Dr. Stephen Straker made part of the I n t e r d i s c i p l i n a r y Committee appointed for t h i s project. Also to Dr. Harold Kasinsky, who agreed to be the external examiner and Dr. Lee Johnson, who acted as Chair in the oral defence. I am s p e c i a l l y grateful to Dr. Stephen Straker, whose help, advise and encouragement were cardinal in the transformation of the early drafts into t h i s , the f i n a l outcome. To him I would l i k e to dedicate any contribution existing in thi s e f f o r t . I g r a t e f u l l y acknowledge the support of External A f f a i r s and International Trade Canada (Government of Canada Awards) who provided a Research Scholarship and to the International Council for Canadian Studies for i t s administration. The "Fondo Colombiano de Investigaciones C i e n t i f i c a s y Proyectos Especiales 'Franciso Jose de Caldas'" of Colombia provided part of the a i r fares for my displacement to Vancouver. v i i i INTRODUCTION The t i t l e i t s e l f looks l i k e a short introduction, but a proper one is necessary to explain i t . Since the S c i e n t i f i c Revolution man has been increasingly thinking of himself, and a l l any other l i v i n g organisms as well, as various kinds of machines. Such comparison with a machine was sometimes e x p l i c i t l y stated -- although rarely was i t s scope c a r e f u l l y examined -- but on other occasions the metaphor was not openly expressed and to reveal i t a degree of perspicacity is needed. The present essay i s an attempt to uncover the pervasive presence of what I term the 'machine metaphor' behind the di f f e r e n t views of what l i v i n g organisms are and how they work. To achieve my purpose I took some recognized milestones in the history of ideas about the inner workings of organisms: the proposals of the early mechanicists during the S c i e n t i f i c Revolution, Lavoisier's view of resp i r a t i o n as combustion, the f i r s t coherent description of the human body as a chemical machine attempted by Liebig and the suggestion that the chemical ix accomplishments in l i v i n g beings are the res u l t of fermentation-l i k e processes. After energy became the unifying concept of physical sciences and machines began to be analyzed as transducers, the conversion of chemical energy into mechanical energy turned out to be a central issue of the treatment of an organism as a chemical machine. That is why I devote a rather large portion of t h i s study to analyze the models suggested to explain the muscle, the prototype of a chemical machine. After a l l , the term 'machine' is c l o s e l y associated with macroscopic movement. The conversion of chemical energy into mechanical energy without the intermediation of heat -- as the process was found to occur in l i v i n g organisms — was explained for decades using models belonging to the f i e l d of c o l l o i d s . The t h i r d chapter is devoted mainly to that period during the f i r s t decades of the present century during which the study of c o l l o i d a l behavior was considered to be the right path to unravel most of the mysteries of v i t a l processes. The dismissal of the c o l l o i d a l approach after the acceptance of the existence of p a r t i c u l a r kind of macromolecules in the c e l l marks the entrance of our modern approach, which in the l a s t chapter I describe as the period of the molecular machine . X As can be deduced from t h i s short summary, the undertaking of describing the 'machine metaphor' at work i s confined within the contrivance aspects of the metaphor. That i s , I treat the machine mostly as an apparatus, a physico-chemical arrangement of parts. Neither the purposeful feature emerging from the fact that i t is a contrivance arranged to execute a task previously foreseen, nor the harmonic working of i t s operation, are dealt with here. Metaphors r e l a t i n g these two aspects — purposefulness and harmonic operation -- with those physiological phenomena encompassed under the broad category 'homeostatic mechanisms', not to say the assimilation of the human brain to a computer, are r e g r e t f u l l y l e f t aside. The only reason i s time. F i n a l l y , the fact that the study is r e s t r i c t e d to the history of ideas does not mean at a l l that in p r i n c i p l e I look with indifference other aspects of the s c i e n t i f i c endeavor. I just believe that the approach followed in t h i s essay establishes a coherent narrative, opening wide and interesting lines of research to pursuit l a t e r . Moreover I claim that i t throws i n s i g h t f u l views on the question of the construction of meaning of s c i e n t i f i c theories. 1 1. ON METAPHOR There i s a m y s t e r i o u s wisdom by which phenomena among themselves d i s p a r a t e can be c a l l e d by analogous names, j u s t as d i v i n e t h i n g s can be d e s i g n a t e d by t e r r e s t r i a l terms, and through e q u i v o c a l symbols God can be c a l l e d l i o n or l e o p a r d ; and death can be c a l l e d sword; j o y , flame; flame, death; death, abyss; abyss, p e r d i t i o n ; p e r d i t i o n , r a v i n g ; and r a v i n g , p a s s i o n . Umberto Eco: The Name of t h e Rose 1.1 INTRODUCTION From the beginning of his existence as a conscious being man has wondered about his most astonishing t o o l : language. Western thought, from Plato's cave to Sapir and Whorf has speculated about the l i m i t s language imposes on our a b i l i t y to understand the world. 1 Are we trapped in the logic we use to communicate our 1 L i n g u i s t i c r e l a t i v i t y , that i s , the idea that language determines the conceptual scheme of individuals i s associated mainly with the names of Edward Sapir and Benjamin Lee Whorf, and the idea is commonly dubbed the Sapir-Whorf hypothesis. 2 ideas, or does th i s l o g i c just mirror some sort of 'world's structure'? Are not we losing important insights into nature's lawfulness with our logic of communication? How can we endeavor to understand what we s t i l l do not understand using the language and theories b u i l t up out of what we already know? Are theories semantic-free, i . e . , is the language used in science only a conveyor of information and theoreti c a l statements just l o g i c a l propositions, or should we adopt the view that we use language as a sort of organ of reception, not only a conveyor of information? Do the categories embedded in discourse l i m i t the possible categories of thought? In summary, What is the relationship between language and the world? These, or some of these, are hard questions to answer which psychologists, anthropologists, philosophers of language, philosophers of science and plain philosophers have been engaged in deep disputes. Some of these can be stated in questions involving the term 'metaphor', such as: Can metaphor be considered as a cognitive device? Is there a l i t e r a l language, as compared to a metaphorical one? Some decades ago metaphor was a subject matter only for rhetoric and l i t e r a r y c r i t i c i s m , and i t was usually considered as an intentional misrepresentation of the world. On the other hand, in the philosophy of science models and analogies were considered as tools r e s t r i c t e d to what Hans Reichenbach c a l l e d the "context of 3 discovery". Under the program of l o g i c a l empiricism, the role of philosophers of science was confined to 'cleansing' science from meaningless statements and rendering s c i e n t i f i c theories as semantically-free l o g i c a l structures. The meaning of the non-l o g i c a l terms used in a s c i e n t i f i c theory, either neologisms invented ad hoc as 'operon' or the vocabulary borrowed from everyday language should be given only by the l o g i c a l web of concepts or by some sort of rules allowing for an observational interpretation. After the advent of other strands of philosophical analysis and the c r i t i q u e directed against this so-called 'received view' of the l o g i c a l empiricists, the attention paid to metaphor changed noticeably, and l i t e r a t u r e in the philosophy of science is nowadays flooded with references to i t . = In t h i s chapter I w i l l make e x p l i c i t some fundamental points concerning the grounds for and consequences of using the notion of metaphor to c l a r i f y questions about the production, v a l i d a t i o n 2 As Geoffrey N. Cantor affirms, "Metaphor has during the l a s t couple of decades become a contentious subject among philosophers" [Cantor, 1982]. In the same c o l l e c t i o n of a r t i c l e s , Jan V. Golinski [Golinski, 1982] mentions as landmarks in the awakening of the new interest on the language of science the work of H.G. Gadamer, Jacques Derrida and Richard Rorty in the philosophy of language, and T.S. Kuhn and M. Foucault in the history and philosophy of science. In p a r t i c u l a r d i s c i p l i n e s , G. Canguilhelm has approached some aspects of the history of biology following a similar approach, and in C r y s t a l . Fabrics and Fields Donna Haraway examined a c r u c i a l period for the history of modern embryology under the guide of metaphor analysis [Haraway, 1976]. 4 and use of s c i e n t i f i c theories. In other words, I am going to use 'metaphor' as a metaphor to account for some features of s c i e n t i f i c theories and explanations. 1.2 THE L I T E R A L AND THE METAPHORICAL The most recognizable feature of a metaphor is the juxtaposition of two domains: a word or phrase is used in a place (second domain) where i t s l i t e r a l meaning ( l i t e r a l in a f i r s t domain) does not f i t exactly. The "semantic anomaly" [McCormack, 1985] originates a tension which could be used as a symptom that a metaphor is present, were i t not for the fact that a persistent use exhausts the metaphor's unconventional feature. Phrases or words that once were able to cause s t r a i n die as source of tension, becoming new entries in the d i c t i o n a r i e s . 3 3 For instance, people are not aware of the large number of anthropomorphic metaphors present in everyday language: the leg of a table, the arms of a chair are but two examples. The etymology of words i s usually a source of information about the s o c i e t i e s where a word was originated, as when we know that 'school' comes from a Greek word denoting what today we c a l l ' l e i s u r e ' . Etymological exploration can also show the deep philosophical problems behind the use of some words. In the case of the verb 'to be', for example, Ju l i a n Jaynes t e l l s us: "Even such an unmetaphorical-sounding word as the verb 'to be' was generated from a metaphor. It comes from the Sanskrit bhu, 'to grow, or make grow', while the English forms 'am' and ' i s ' have evolved from the same root as the Sanskrit asmi, 'to breathe 1. It is something of a lovely surprise that the irregular conjugation of our most nondescriptive verb i s thus a record of a time when man had no independent word for 'existence' and could only say that something 'grows', or that i t 'breathes'" [Jaynes, 1976]. Sometimes people seem to pay more attention than is sensible to the dormant metaphors, as when some r a d i c a l feminists struggle to 5 Why is the second domain described in terms of the f i r s t instead of being referred to l i t e r a l l y ? One possible answer could be that in some instances the available vocabulary is i n s u f f i c i e n t and pointing or drawing are not allowed (catachresis), as in the use of the word 'orange' to denote a color. Another possible answer could be that for aesthetic reasons an author prefers an unusual term of a periphrasis to say something that he could have said d i r e c t l y . Although situations in which these answers account for the use of a metaphor ex i s t , they far from exhaust the apparent cognitive and emotional achievements of the juxtaposition of meanings in paradigmatic metaphors. Take the c l a s s i c a l example: "Man is a wolf". "Wolf" refers l i t e r a l l y to "any of a large group of f l e s h -eating doglike mammals widely d i s t r i b u t e d throughout the Northern Hemisphere" (Webster's Collegiate Dictionary) and does not map completely onto Homo sapiens. Which of the many anatomical, physiological or behavioral features of 'wolf' is the author aiming to ascribe to 'man* depends on the context of what i s being said and es p e c i a l l y on the set of "associated commonplaces" between the concepts 'man' and 'wolf' when taken l i t e r a l l y in a parti c u l a r culture."* In l i t e r a r y contexts the author w i l l play change 'chairman' or 'mankind' for something less male-dominant. "* The expression "associated commonplaces" i s Max Black's, in his Models and Metaphors [Black, 1962]. Black reminds us that in cultures where wolves are sacred animals the metaphor w i l l with the analogies and disanalogies to evoke in the reader some s p e c i f i c emotions, r a r e l y planning to close the interpretations. Aside from suggesting s i m i l a r i t i e s , the metaphor opens a universe of vagueness and assumes t h i s as the ris k of trying to say something new.8 A metaphor i s an exploration of novel interpretations, of new possible meanings for already existing words and concepts, suggested by an author when he introduces an i n t e l l i g i b l e anomaly in l i t e r a l meanings. The metaphor not only produces i t s e f f e c t by suggesting new perceptions about the second domain; i t also has the power of af f e c t i n g meanings in the f i r s t domain. In the example above, not only 'man' i s exposed to reinterpretations; 'wolf* i s , too. The metaphor is successful i f i t evokes new insights — the tension is attached to the novelty — i f i t awakens in the hearer or reader a net of interconnections or s i m i l a r i t i e s between the two domains. The reader w i l l say he 'understood' the author's intentions i f the text is able to have a quite d i f f e r e n t e f f e c t . Konrad Lorenz used to t e l l that when two doves are confined u n t i l starvation they w i l l fight u n t i l one eats the other, while two wolves w i l l never behave in that way. Were thi s everyone's knowledge the dove as metaphor for peace would lose i t appeal. a Morse Peckham, in his Foreword to Turbayne's The Myth of  Metaphor [Turbayne, 1970] puts metaphor in the forefront of language construction: "I was convinced that metaphor is not only a normal semantic mode but a mode essential for the existence and above a l l the extension of the semantic functions of language. It is the only way we have for saying something new". 7 produce a p a r t i a l overlapping of the reader's views about both domains. 1.3 THE RECEIVED VIEW OF S C I E N T I F I C THEORIES AND EXPLANATION Are these considerations of any relevance when we analyze the way in which theories are suggested, proposed, invented and defended by s c i e n t i s t s ? Many people w i l l agree that they are indeed, but within the context of discovery, not in the context of j u s t i f i c a t i o n . In fact, does Kekule's dream about a snake b i t i n g i t s t a i l have any importance for understanding the benzene ring? In the context of j u s t i f i c a t i o n , i t would be argued, we are engaged in the task of finding or arranging the evidential support for a theory. J u s t i f i c a t i o n would not be the realm of imagination, where the individual s c i e n t i s t after a t r i a l and error procedure with analogies, extensions, generalizations, models, aesthetical considerations and so on, envisions a theory or an explanation for a phenomenon. A l l this can be of interest only to biographers, psychologists, or some historians of science hardheadedly stuck with the history of ideas. The judgement of a p a r t i c u l a r s c i e n t i f i c community should barely be influenced by these things, i f influenced at a l l . 8 There are, however, other circumstances in which the relevance of metaphor-like processes i s not so e a s i l y disposed of. Is the benzene ring i t s e l f a 1 i t e r a l description about a r e a l , existing molecule? Is the 'slippery' electron a p a r t i c l e , a wave, sometimes the former and sometimes the l a t t e r , both, or only a mathematical f i c t i o n ? Are men jealous l i k e geese, or geese jealous l i k e man? s With their r e j e c t i o n of these sorts of •unobservables 1, e a r l i e r p o s i t i v i s t s ended up denying not only the existence of molecules, but some of them even suggested that an appeal to f i c t i o n s l i k e these in sound science was i l l e g i t i m a t e . As for the l o g i c a l empiricists, harmonizing the unavoidable approval of unobservables with the aim of barring from science statements devoid of empirical content was one of th e i r goals. They had to acknowledge that one of the outstanding features of s c i e n t i f i c theories, p a r t i c u l a r l y in physics, their great 6 It i s a well documented episode in the history of science the strong resistance against Van•t Hoff's suggestion that molecules have shape. Kolbe, the editor of the Journal fur  praktische Chemie, where Van't Hoff's theory of the asymmetrical carbon appeared for the f i r s t time in German (1877), wrote about the theory using b i t t e r statements l i k e the following: "'The arrangement of atoms in space', by Messr. Van't Hoff and Hermann ... teems with fantastic t r i f l e s . A Dr. Van't Hoff who is employed at the Veterinary School in Utrecht appears to find exact chemical research not suited to his taste. He deems i t more convenient to mount Pegassus (evidently loaned from the Veterinary School) and to ... proclaim how to him on the chemical Parnassus ... the atoms appeared to be arranged in the Universe... The prosaic chemical world found l i t t l e taste in these hallucinations" (quoted in [Van't Hoff, 1967]). 9 exemplar, is the fact that those very theories contain unobservables. If a theory of science i s going to give an account of what science is and what s c i e n t i s t s do, these unobservables cannot be neglected. The problem, then, was how to assign to them a precise meaning, and the solution was looked for in the rela t i o n s h i p between unobservables and observables. But the reduction of the o r e t i c a l statements to statements in a purely observational vocabulary could not be done just by d e f i n i t i o n s . According to Carnap, "there is no way that a theo r e t i c a l concept can be defined in terms of observables. We cannot give a r e a l l y adequate d e f i n i t i o n of the geometrical concept of ' l i n e ' by r e f e r r i n g to anything in nature..." [The] axiomatic terms -- 'electron', ' f i e l d ' , and so on — [of a postulate system in physics] must be interpreted by correspondence rules that connect the terms with observable phenomena. This interpretation i s necessarily incomplete. Because i t is always incomplete, the system is l e f t open to make i t possible to add new rules of correspondence. Indeed, this is what continually happens in the history of physics [Carnap, 1966 ] . Observational vocabulary is not applicable to the o r e t i c a l vocabulary. Instead, "correspondence rules" have to be formulated between th e o r e t i c a l terms and observable terms for some of the former, so they can be contrasted with experimental facts. For example, i f t i s a th e o r e t i c a l term we cannot say that t_ means 'red', because we would be defining a th e o r e t i c a l term with an 10 observable one. A statement such as "a certai n wavelength is. red" makes no sense; one does not say that the wave is red, but rather that i t corresponds to the observable red. Correspondence rules are of the form "whenever property x_ (an observable property, in the example here, red) of an enti t y a. (the radiation coming from a source) i s true, then i t i s also true that 'ta' (the radiation coming from the source has an spe c i f i e d wavelength)." In very general terms t h i s i s Carnap's view of theories as " p a r t i a l l y interpreted axiomatic c a l c u l i " . Any possible meaning for t h e o r e t i c a l terms d i f f e r e n t from their being part of an axiomatic structure and from the meaning acquired in virtue of correspondence rules was e x p l i c i t l y ruled out. (See below for further precision on thi s point.) The account just sketched represents what, following Hilary Putnam, has been c a l l e d the 'received view' of theories. As part of l o g i c a l empiricism i t dominated Anglo-American philosophy of science in the 1940's and 1950's. For many years since, c r i t i c i z i n g the received view has been the main source of s e l f d e f i n i t i o n for many philosophers of science. P a r a l l e l to the received view of theories, the so-called deductive-nomological, or covering-law, model of explanation was developed, mainly by Carl Hempel. According to the model a l l explanations in science have in common the following scheme: a 11 series of statements about phenomena (the explanandum) are said to be explained i f one can l o g i c a l l y deduce them from some singular statements (antecedent conditions) along with some general laws of nature (these two comprising the explanans). The explanation must comply with the following rules: Rl The explanandum must be a l o g i c a l consequence of the explanans R2 The explanans must contain at least one general law R3 The explanans must have empirical content R4 The sentence constituting the explanans must be true According to the received view, then, theories do not spring up as generalizations from experimental data. Theoretical terms could appear as the res u l t of an i n t e l l e c t u a l process properly catalogued under 'imagination 1, a process belonging to the context of discovery. But what constitutes s c i e n t i f i c knowledge are the f i n a l clean statements formalized in propositional structures. Explaining i s fundamentally a l o g i c a l process by which statements describing observations are obtained deductively from a set of statements containing at least one general law. In th i s account, we see, there seems to be no place for anything akin to metaphor. As stated in the introduction, the terms used in science -- force, a t t r a c t i o n , p a r t i c l e , reaction, molecule, competition — and the statements b u i l t with them have a meaning r e s t r i c t e d to their use in s c i e n t i f i c language. If the words or the images coincide with terms or statements in everyday 12 language, i t is just an unfortunate state of a f f a i r s . Supposedly, ideology i s kept out of science with t h i s strategy. 1.4 MODELS IN THE RECEIVED VIEW There are two ways of attaching meaning to th e o r e t i c a l terms. One is given by the l o g i c a l web of axioms (for example, the term "molecule" appearing in a theory may be defined i m p l i c i t l y as "that e n t i t y s a t i s f y i n g such and such axioms and theorems"). The other way is by the correspondence rules c o r r e l a t i n g some theo r e t i c a l terms with observational terms. There are then two sources of 'partialness* in Carnap's idea of " p a r t i a l l y interpreted axiomatic c a l c u l i " : (1) Correspondence rules are not d e f i n i t i o n - l i k e . If one had a d e f i n i t i o n for "molecule" then one would be able to replace the word with i t s d e f i n i t i o n and every sentence would preserve i t s meaning. There is no d e f i n i t i o n as such for theoret i c a l terms because as continuous research unravels more features of the world, more correspondence rules (and hence 'more meaning 1) are attached to a th e o r e t i c a l term. - 7 ^ Carnap asserts even that at the moment one states a d e f i n i t i o n , one has an observable term: "Eventually a point may be reached beyond which there w i l l be no room for strengthening the interpretation of a term by new correspondence rules. Would not the rule then provide a f i n a l , e x p l i c i t d e f i n i t i o n for the term? Yes, but then the term would no longer be t h e o r e t i c a l . It would become part of the observation language" [Carnap, 1966, p. 13 (2) As there is not necessarily a correspondence rule for each unobservable (theoretical) term, some statements can have no meaning attached to them via a correspondence rule. In t h i s description of the attachment of meaning, one of the more conspicuous expressions used by s c i e n t i s t s when they describe th e i r work i s missing: models. Rarely are s c i e n t i f i c theories presented or used as " p a r t i a l l y interpreted axiomatic c a l c u l i " . Normally, they are presented through models. We can say that part of the content of the theory can be v i s u a l l y imagined, and here is where s c i e n t i s t s appeal to models. In i t s more general ( l o g i c a l ) sense a model for a theory i s a set of e n t i t i e s and i t s attributes that s a t i s f i e s the theory. Some authors c a l l t h i s an "interpretation". A model for Newton's law of gravitation could be an imaginary system of p a r t i c l e s a t t r a c t i n g each other according to the inverse-square law and moving according to the three laws of motion. Correspondence rules can then be established between t h i s model and astronomical observations of the spots seen in the sky. Thus, a model for a theory plus the correspondence rules s a t i s f i e s both the axioms and the rules, but can attach additional meanings for t h e o r e t i c a l terms and can attach "meaning" to statements lacking i t in a rigorous view. In this way, the model would be complementing the p a r t i a l interpretation a r i s i n g from considerations (1) and (2) above, 238]. 14 providing at the same time candidates for new correspondence rules. Now, is t h i s view of model licensed in the "received view"? Some followers of l o g i c a l empiricism claim that i t i s . Some antagonists remind them of Carnap's e x p l i c i t prohibition of attaching meaning by ways d i f f e r e n t from correspondence rules and axiomatic s t r u c t u r e . 0 To them accepting a sort of 'meaning' (Nagel writes i t in quotation marks) from an interpretation in terms of a metalanguage — in t h i s case the natural s c i e n t i f i c language — would be l i k e opening the backdoor to l e t in the vagueness against which the core of the l o g i c a l empiricist's program had promised defense. But even i f we accept that through the metalanguage the received view allowed some kind of non-observable interpretation language, undoubtedly i t was very far from being sponsored. The l o g i c a l empiricist account, then, is intended to license t h e o r e t i c a l terms in the philosophy of science. To accomplish t h i s goal while keeping a l l science based on 'safe sense data', the d i s t i n c t i o n between "theoretical terms" and "observational e Nagel, for example, formulates three components of the theory: the axiomatic c a l c u l i , the correspondence rules and "an interpretation of model for the abstract calculus, which supplies some fle s h for the s k e l e t a l structure in terms of more or less familiar conceptual or v i s u a l i z a b l e materials" [Nagel, 1961, p. 90]. Although Nagel can be considered an advocate of the l o g i c i s t view of l o g i c a l empiricism, his inclusion of models as part of the apparatus for attaching meaning is quite d i f f e r e n t from Carnap's almost complete dismissal of them. terms" was drawn. 9 By axiomatizing s c i e n t i f i c theories while attempting a 'logic of induction*, science was thought to be put on a safe basis. Curiously enough, among a l l the c r i t i c i s m the received view and i t s c o l l a t e r a l developments suffered, the ones that i n f l i c t e d more severe damage were directed against the dichotomy observational - t h e o r e t i c a l and against the claim that s c i e n t i f i c theories are axiomatic s t r u c t u r e s . 1 0 As i s p a r t i c u l a r l y clear in i t s treatment of models, l o g i c a l empiricism s t r i v e d to separate the context of discovery -- which in fact i s more l i k e the context in which theories are a c t u a l l y used -- from the context of j u s t i f i c a t i o n , the former f u l l of everyday experience and ordinary use of language; the l a t t e r , 9 The need to license terms in s c i e n t i f i c theories i s a philosophical problem. S c i e n t i s t s do not ask philosophers to issue any sort of licence. 1 0 A Lakatosian account of the r i s e and f a l l of the l o g i c a l empiricist's research program f i t s very well with i t s development. The program was born with two aims — coinciding with i t s greatest anomalies. To show that s c i e n t i f i c theories can be studied as axiomatic structures, and to allow for the presence of unobservables. To deal with the l a t t e r l o g i c a l empiricism sponsored the d i s t i n c t i o n between observational and t h e o r e t i c a l . But in spite of the fact that they were always discussed, the anomalies did not stop the research program u n t i l the program i t s e l f f a i l e d to produce results remarkable enough to diminish the s i g n i f i c a n c e of these anomalies. If i t is claimed sometimes that inside science dismissal of a theory comes after a complex switch of view, t h i s feature of theory change must be even more noticeable in the decline of a philosophical school. None of the individual c r i t i c i s m s against l o g i c a l empiricism was by i t s e l f decisive enough to be the cause of i t s dismissal. 16 pure, the realm of l o g i c . 1 1 That was p r e c i s e l y the d i v i s i o n that made 'metaphor* an unacceptable tool to analyze the growth of science. But now, i f the received view has been dismissed and theories are not anymore considered as ' p a r t i a l l y interpreted c a l c u l i ' , what is l e f t as a ' s c i e n t i f i c theory'? As d i s t i n c t from the years of high praise for the received view, today there i s more consensus about what theories are not than about what theories are. Presently, most philosophers of science claim that more attention must be paid to the way theories are used, giving up any i l l u s i o n of constructing safe knowledge based in something akin to pure sense data and giving up any dream of building a logic of induction to account for theory change and development in ' l o g i c a l terms'. x z Terms in s c i e n t i f i c theories are continually open to reinterpretation, a fact acknowledged even in the received view with the extension of meaning through 1 1 If s c i e n t i f i c theories are there only to be f a l s i f i e d the idea that theories are a c t u a l l y used in the context of discovery more than in the context of j u s t i f i c a t i o n i s strange-looking. But theories exist at d i f f e r e n t l e v e l s , and in addition more than one is present in a p a r t i c u l a r research endeavor. For example, the 'enzyme theory' of c e l l processes (see Chapter 3) is used to apprehend, say, data related to the oxidation of foodstuffs, and as a res u l t a theory for t h i s p a r t i c u l a r process w i l l r e s u l t . To some extent the 'enzyme theory' is enduring a f a l s i f y i n g test, but to a much greater extent i t i s being used in a context of discovery to analyze sets of experimental data. It i s supplying the 'glasses' through which a p a r t i c u l a r experiment i s being observed and parametrized. The procedures to relate the results to a model pertaining to oxidation in t h i s cases, as well as to an enzyme theory are anything but closed. 1 2 Stephen Toulmin interpreted the aim of l o g i c a l positivism as that of reducing ' r a t i o n a l i t y ' to ' l o g i c a l i t y ' [Toulmin, 1977] 17 new correspondence rules. Philosophy of Science does not draw anymore a demarcation between science and non-science by barring some class of terms from the former. S c i e n t i f i c theories, of course, must render statements susceptible to comparison with experimental r e s u l t s , notwithstanding the fact that there are not straightforward rules for a decision procedure following a contradiction between experimental results and predictions coming from the theory. Having almost abandoned the task of establishing formal rules to d i f f e r e n t i a t e the statements comprising s c i e n t i f i c theories from a l l other statements that are the product of man's faculty of thinking, modern theories of science have ruptured t h e i r link with old claims that science offers the unique route to the l i t e r a l description of man and the world. The difference between science and other i n t e l l e c t u a l endeavors is clearer i f we look at attitudes: some s c i e n t i s t s struggle to close their favorite metaphors, while others s t r i v e to change the metaphors by shaking t h e o r e t i c a l structures at the loose ends. 1.5 MODELS, METAPHORS AND PARADIGMS Let us b r i e f l y consider some situations where the word 'model' i s invoked: Faraday's lines of force, Ising's model of phase t r a n s i t i o n s , the hydraulic model of e l e c t r i c current, the e l e c t r i c a l c i r c u i t model of an economic system, the scale model of an airplane, the Darwinian model for the survival of theories 18 in science, the covering-law model of explanation, the b a l l s and s t i c k s models of molecules, the Briggs-Haldane mathematical model of enzyme k i n e t i c s , the l i q u i d drop model for the nucleus of the atom and so forth. Models are enormously varied and taxonomies of d i f f e r e n t kinds are possible. According to i t s "sense", Suppe [Suppe, 1977] considered models to be either mathematical or iconic, the former ones the s t r i c t l y l o g i c a l , the l a t t e r r e f e r r i n g to concrete objects. Conversely, Black mentions scale models, those icons presuming r e l a t i v e geometrical proportions, analogue models, reproducing some st r u c t u r a l relationships in the o r i g i n a l , mathematical models, sometimes just a mathematical treatment and sometimes an intended physical and/or mathematical s i m p l i f i c a t i o n , and t h e o r e t i c a l models, those generally describable as or i g i n a t i n g in an analogue model whose objects are idealized by s t r i p p i n g off the negative analogies [Black, 1962]. The favorite example of a theoretical model is Maxwell's set of equations for the electromagnetic f i e l d . I n i t i a l l y conceived as equations describing s t r e s s / s t r a i n relations of a r e a l l y existing mechanical ether, the model was stripped of i t s uneasy features u n t i l the ether transmitting the waves simply disappeared. Electromagnetic waves ended up being vibrations of nothing, and each point of the space was accepted as the place of an e l e c t r i c f i e l d whose i n t e n s i t y and d i r e c t i o n i s described by the set of equations. No reference is made anymore to the ether model. In almost a l l cases, the models fades away while at the same time the theory i t s e l f is more and more accepted. The waning of the o r i g i n a l model i s at the heart of the idea that there i s r e a l l y no model here at a l l and that the description is d i r e c t and l i t e r a l . A mixture of t r a d i t i o n and success has produced the f e e l i n g that some theories allow us to describe and explain the world as i t i s , in i t s natural categories without any models. Today everyone is at r i s k of waking up after a bad Lucretio-Cartesian night with the v i s i o n that everything r e a l l y i s just matter and motion. The most clear symptom that nowadays one p a r t i c u l a r approach has acquired a monopoly on the status of the l i t e r a l i s that 'finding the mechanism' and 'explaining' are often considered to be equivalent. Ingenuousness about the vocabulary being used i s a d i r e c t road to becoming a victim of a metaphor instead of i t s u s e r . 1 3 'Finding the mechanism' i s an expression whose long history should make us aware to take i t with caution. But i t s d a i l y and a l l pervasive use has transformed i t into a dormant metaphor, as i f i t were another common element of our natural language. 1 3 One of the central ideas of Colin Turbayne's The Myth of  Metaphor is that unawareness of the existence of metaphors underlying alleged l i t e r a l description w i l l turn the user of the theory into a victim of the hidden metaphor [Turbayne, 1970]. When no e x p l i c i t reference is made to a model, we must suspect the presence of categories that once were mere challengers of other accepted c l a s s i f i c a t i o n s , but that are now so deeply rooted that they do not seem at a l l to be suppressing other possible approaches. They are the only possible approach. Max Black c a l l s them 'conceptual archetypes'. They are: systematic repertoirets] of ideas by means of which a given thinker describes, by analogical extension, some domain to which those ideas do not immediately and l i t e r a l l y apply. [Black, 1962] Reconstructing such kinds of underground archetypes amounts to finding "a l i s t of key words and expressions, with statements of their interconnections and their paradigmatic meanings in the f i e l d from which they were o r i g i n a l l y drawn" [Black, 1962] In order to show what he means by conceptual archetypes, Black makes use of Stephen Pepper's penetrating e f f o r t to discover deep-rooted c o n s t i t u t i o n a l metaphors. Pepper t r i e s to make a taxonomy of the highly variable "zoology" of suggested worldviews in the hi s t o r y of philosophy. 1** By using what he named "root metaphor theory" Pepper concluded that behind the great variety of world hypotheses there are repeated themes, so that the successful ones can be f i t t e d into a small taxonomy. "The root metaphor theory i s simply a recognition of the fact that there Pepper c a l l e d these worldviews "world hypotheses", and defined them as those "products of knowledge ... that ... cannot reject anything as i r r e l e v a n t " [Pepper, 1961]. 21 are schools of philosophy... but philosophical imagination is not as p r o l i f i c as many claim" [Pepper, 1961, p. 328]. The method [of world hypothesis construction from a root metaphor] in p r i n c i p l e seems to be t h i s : A man desiring to understand the world looks about for a clue to i t s comprehension. He pitches upon some area of common-sense fact and t r i e s i f he cannot understand other areas in terms of t h i s one. The o r i g i n a l area becomes then his basic analogy or root metaphor. He describes as best he can the c h a r a c t e r i s t i c s of t h i s area, or, i f you w i l l , discriminates i t s structure. A l i s t of i t s s t r u c t u r a l c h a r a c t e r i s t i c s becomes his basic concepts of explanation and description. We c a l l them a set of categories. In terms of these categories he proceeds to study a l l other areas of fact whether u n c r i t i c i z e d or previously c r i t i c i z e d . He undertakes to interpret a l l facts in terms of these categories. As a res u l t of the impact of these other facts upon his categories, he may q u a l i f y and readjust the categories, so that a set of categories commonly changes and develops. Since the basic analogy or root metaphor normally (and probably at least in part necessarily) arises out of common sense, a great deal of development and refinement of a set of categories i s required i f they are to prove adequate for a hypothesis of unlimited scope. Some root metaphors prove more f e r t i l e than others, have greater power of expansion and adjustment. These survive in comparison with the others and generate the r e l a t i v e l y adequate world theories [Pepper, 1961, p. 91]. Pepper found four "adequate world theories", which he dubbed formism, mechanism, contextualism and organicism. l B Although Black seems to endorse Pepper's conclusions, nonetheless the former does not challenge the existence of a l i t e r a l descriptions in science. His suggestion to look for the x a One interesting use of Pepper's "root metaphor theory" can be found in The Vit a l i s m of Hans Driesch, by Horst H. Freyhofer [Freyhofer, 1982]. 22 archetypes is limited to "[those] cases where we have, as i t were, an i m p l i c i t ... model" [Black, 1961, p.239]. Presumably, one is to understand by Black's reluctance to say that a l l theories have conceptual archetypes that he believes there are realms describable or explainable in their own terms, in contrast with some domains where certain "ideas do not immediately and l i t e r a l l y apply" ( i b i d . ) . This sort of l i t e r a l i t y i s surely in the mind of some 'soft c r i t i c s ' of the use of models in science ( l i k e Braithwaite) who accept th e i r use, but argue that "the price of [their use] i s eternal v i g i l a n c e " . I would agree with them, but only after having obtained an answer to the question: When i s eternal vigilance not necessary? I would suggest we must extend our vigila n c e to any theory, those with e x p l i c i t models and those with i m p l i c i t archetypes. In thi s way a l l s c i e n t i f i c conceptual-i z a t i o n would be covered by the c a l l of prudence i m p l i c i t in the warning that hidden assumptions, very l i k e l y o riginating in some kinds of metaphors, are within the c i t a d e l of science. This recognition, however, does not deny the fact that d i f f e r e n t schools may allocat e the watchmen to d i f f e r e n t places. The f e e l i n g of l i t e r a l i t y produced by these s c i e n t i f i c theories which make no clear declaration that a model or metaphor i s being used is heightened by the covering-law account of explanation. In fact, the l a t t e r ' s emphasis on lo g i c pretended to circumvent any 23 appeal to models or analogies. Hempel d e l i b e r a t e l y contested N. R. Campbell's insistence on the c r u c i a l role of analogy when the l a t t e r wrote: "In order that a theory may be valuable i t must ... display an analogy" [Campbell, 1920, p. 129]. For Campbell the analogy was far from being a mere aid in formulating a theory. The dynamical theory of gases, for example, was accepted not because i t provided a general formal structure from which some experimental laws previously known could be deduced — for Campbell producing such sort of l o g i c a l structures is extremely easy — but because the theory provided a successful analogy. More recently, Mary Hesse, repeating Campbell, suggested that for t h e o r e t i c a l explanations "the deductive model should be modified and supplemented by a view of t h e o r e t i c a l explanation as metaphorical redescription of the domain of the explanandum" [Hesse, 1966, my emphasis]. In t h i s way, she claims, some inadequacies of the covering-law model would be amended, as follows: (1) The statement describing the fact to be explained in the observational domain is not obtained exactly from the l o g i c a l deduction. What occurs i s that a deduced statement i s used to interpret the f i r s t domain, an interaction of meanings properly belonging to the semantic figure we have c a l l e d metaphor. 24 (2) There is no deductive r e l a t i o n between the explanans and the explanandum, for there i s the mediation of correspondence rules. These 'rules' would be better understood as part of a metaphorical r e d e s c r i p t i o n . 1 6 (3) The strong sense of prediction — extension of the theory to new domains by prediction of laws not l o g i c a l l y contained in the theory and e x p l i c i t correspondence rules — requires additions to the correspondence rules. There is no rat i o n a l method for adding new rules. They become a useless concept. "In the metaphoric view... since the domain of the explanandum i s redescribed in terminology transferred from the secondary system, i t is to be expected that the o r i g i n a l observation language w i l l both be shi f t e d in meaning and extended in vocabulary..." [Hesse, 1966]. The metaphorical view, then, does not require additional consideration of the Idea of correspondence rules. There remains, of course, one important question: Does i t make any sense to bring in the notion of metaphor, taking the ris k of converting i t into just another name for the already well discussed 'model'? In t h i s way, Hesse i s eliminating the theoretical/ob-servational d i s t i n c t i o n : "There is one language, the observation language, which l i k e a l l natural languages i s continually being extended by metaphorical uses and hence yields the terminology of the explanans" [Hesse, 1966]. 25 The question i t s e l f reveals one of the outstanding features of metaphor-like processes. When we import the term •metaphor*, whose l i t e r a l realm belongs to a r t , with the aim of using i t in an examination of the process of constructing the meaning of categories in natural sciences, we engage ourselves in a comparison of conceptualization in science with the processes of the extension of meaning in language i t s e l f and with the creative uses of language in l i t e r a t u r e . Once we have decided to use the term 'metaphor * to study what s c i e n t i s t s do when they look for explanations, we have to decide i f we are going to take the term l i t e r a l l y . i r Poetry and science are not the same endeavor. The exploration of the negative analogies should show the usefulness of attempting to understand s c i e n t i f i c theories by considering ideas in science as evolving through metaphor-like processes. If we do t h i s — i f the metaphor has been successful — new insights not only on how s c i e n t i f i c theories are constructed and validated, but also on the character of metaphor in l i t e r a t u r e w i l l be gained. X 7 We should not f e e l discouraged by the fact that 'metaphor' is going to be a metaphor to account for s c i e n t i f i c theories. The l o g i c a l empiricist account, that s c i e n t i f i c theories are pure mathematical structures, is also a metaphor tKuhn, 19773. I think in addition that Colin Turbayne i s right when he claims that behind Newton's approach there is the idea that 'p r i n c i p l e s ' such as are used in l o g i c a l analysis can be used to lead us to 'natural p r i n c i p l e s ' whereby to analyze nature. That i s , Newton uses a metaphor in which the l i t e r a l realm is the realm of l o g i c , to t r y to discover in the world a l o g i c a l structure. 26 There is an evident resemblance between model and metaphor. According to Black, a model would be a "sustained and persistent metaphor". But while in l i t e r a t u r e the interaction is usually l e f t to commonplaces requiring for the creator only proverbial knowledge, in science the creator requires "prior control of a well-knit s c i e n t i f i c theory i f he i s to do more than hang an a t t r a c t i v e picture on an algebraic formula" [Black, 1962]. Turbayne stresses the fact that in models the analogies should be s p e c i f i e d [Turbayne, 1970], while Hesse states that " i n s c i e n t i f i c contexts the primary and secondary systems may both be highly organized by networks of natural laws" [Hesse, 1966]. For example, i f one is to apply an hydraulic model for the e l e c t r i c current in metals, the behavior of systems in both realms must be f a i r l y well known. She points out two other negative analogies: "We can perhaps signal the difference by speaking in the case of s c i e n t i f i c models of the (perhaps unattainable) aim to find a •perfect metaphor'; in poetry, metaphors may be i n t e n t i o n a l l y (often, not always) imperfect...". On the other hand, " s c i e n t i f i c models ... may be i n i t i a l l y unexpected, but i t is not th e i r chief aim to shock..." [Hesse, 1966]. We can see that the differences are not sharp -- "models may be", "metaphors perhaps are". There exists a kind of ' i l l u s t r a t e d poetry' where the author consciously explores d i f f e r e n t faces of a metaphor. 'Shocking' i s not necessarily an e x p l i c i t purpose of a metaphor in l i t e r a t u r e -- better, we say that the 'shock' is produced by the suggestion of a novel interpretation -- while s c i e n t i f i c theories change in a tense environment of imprecise meanings. On the other hand, we cannot neglect the presence of root metaphors — undoubtedly not c a r e f u l l y knitted — at the base of t h e o r e t i c a l models. Models are metaphors in the sense that there i s transfer of meaning between d i f f e r e n t domains and that they contain open and consequently imprecise analogies. The tension inherent in t h e i r use i s noticeable during periods of theore t i c a l r i v a l r y and remains v i s i b l e in the loose ends. There, l o g i c a l empiricism saw a place for adding new correspondence rules to a s o l i d , almost immovable theory, while the metaphor approach stresses the resemblance with the process of the construction of meaning pertaining to a l l form of knowledge. F i n a l l y , I w i l l add that models do not pretend to have an emotive content, and that, unlike what happens in a r t , they are stated as speculative instruments to be taught, learned, accepted and methodically explored by successive generations. These l a s t features accentuate the differences due to the kind of community to which the metaphor i s addressed. Inside the s o c i a l processes of v a l i d a t i o n and perpetuation, s c i e n t i f i c terms share a l l the uncertainties suffered by the meanings of any terms, so well described by Hesse: 28 To understand the meaning o£ a descriptive expression is not only to be able to recognize i t s referent... but also to c a l l to mind the ideas, both l i n g u i s t i c and empirical, that are commonly held to be associated with the referent in the given language community. [Hesse, 1965] We cannot help but see Kuhn's notions of paradigm, exemplar and conceptual s h i f t in the metaphor approach. 1 3 Something having the properties of metaphor i s often c a l l e d upon, states Kuhn, not only when a new term is introduced in the vocabulary of science; " i t i s also c a l l e d upon when such terms -- by now established in the common parlance of the profession -- are introduced to a new s c i e n t i f i c generation" [Kuhn, 1977] . Further on he states: "However s c i e n t i s t s apply terms l i k e 'mass', ' e l e c t r i c i t y ' , 'heat', 'mixture' or 'compound' to nature, i t i s not o r d i n a r i l y by acquiring a l i s t of c r i t e r i a necessary and s u f f i c i e n t to determine the referents of the corresponding terms" [Kuhn, 1977]. 1 9 1 3 Kuhn himself e x p l i c i t l y acknowledged t h i s point. After accepting that the term 1 Paradigm' had led to many misunderstandings, he stated: "No aspect of my viewpoint has evolved more since the book was written... We approach the problem in the same s p i r i t including a common conviction of the relevance of the philosophy of language and of metaphor" 1 9 An uncommonly open statement of the relevance of non-formal meaning of s c i e n t i f i c concepts is found in the Prologue to Kurt Gottfried's and Victor Weisskopf's book Concepts of P a r t i c l e  Physics, Vol. I: "physics has both a written and an oral t r a d i t i o n . I n t u i t i v e modes of thought, inference by analogy and other stratagems that are used in the e f f o r t to confront the unknown are transmitted from one generation of p r a c t i t i o n e r s to the next by word of mouth. After the work of creation is over, the results are recorded for posterity in a l o g i c a l l y impeccable form, but in language that is often opaque. The beginner is 29 The meaning of s c i e n t i f i c terms and theories to the oncoming generation w i l l be captured through the exposure to shared exemplars, not by e x p l i c i t rules for attaching the theory to new sit u a t i o n s . Instead of correspondence rules, Kuhn suggests "resemblances between apparently disparate problems" [Kuhn, 1979]. It appears c l e a r l y that in Kuhn's view, the kind of openness present in the cognitive processes e x p l i c i t l y acknowledged as metaphors w i l l provide a better account for the way theories are used than fixed theories with a changing number of correspondence rules. In the following chapters I am going to trace the evolution of ideas about the prototypical features of organic processes occurring in the b i o l o g i c a l i n d i v i d u a l , paying attention to the e x p l i c i t and i m p l i c i t references made to 'mechanisms' and 'machines'. Besides devoting attention to the open allusions to the realm of man-made contrivances, I w i l l also endeavor to find hidden assumptions, that i s , aspects of the undeclared use of the expected to absorb t h i s written t r a d i t i o n , and only the survivors of t h i s t r i a l - b y - o r d e a l are admitted to c i r c l e s where the oral t r a d i t i o n i s current.... We believe that t h i s t r a d i t i o n plays an essential role not only in the creation of physics, but also in the search for new understanding" [ G o t t f i e l d , Weisskopf, 1984, p v i i ] . 30 machine metaphor hiding behind the explanations suggested for part i c u l a r physiological processes. 31 2. FROM CLOCKWORKS TO CHEMICAL MACHINES 2.1 INTRODUCTION As one of the entries for 'mechanism' a dictionary w i l l t e l l us that the term refers to a doctrine according to which a l l phenomena related to l i v i n g beings are just manifestations of physical and chemical laws. 2 0 Etymologically the term comes from the greek mechane -- machine or contrivance. Apparently, the o r i g i n a l r e l a t i o n of the term with machines was abandoned a long time ago and can be found, i f at a l l , only as a r e l i c , a c u r i o s i t y , when observers interested in the evolution of ideas move among the o r i g i n a l sins of today's t r a d i t i o n a l approaches. 2 1 2 0 See, for example, Webster's New World Dictionary, The World Publishing Company, Cleveland and N. York, 1966. 2 1 In her book On the nature and o r i g i n of l i f e Hilde S. Hein, for example, remarks that the thinkers belonging to the period of the S c i e n t i f i c Revolution were limited by the knowledge and the simple machines then available for explanation or analogical extension to the organic realm: "The mechanism of the XVIIth and XVIIIth was dominated and limited by the character of contemporary science" [Hein, 1971, pg 81]. She is ri g h t , but I am af r a i d that to her XXth century s c i e n t i s t s are neither limited by 32 As I s h a l l show, open allusions to machine-like operations have been always present when the most fundamental features of l i v i n g creatures are under scrutiny. But more interesting are some hidden assumptions of the reductionist approach that in d i f f e r i n g degrees remind us either of contemporary technology or just of those everyday exemplars of evident mechanical behavior. At the same time, when hypotheses about particular physiological events were advanced under the view that those events were caused by a peculiar organization of matter moving according to knowable rules, i t was not forgotten that the phenomena are parts of l i v i n g creatures. A very appropriate s t a r t i n g point i s the so-called S c i e n t i f i c Revolution of the XVIIth century, when the present meaning of 'mechanism' was established, and when physiological processes began to be analyzed as mechanical interaction of the matter making up the constituent parts of organs and substances. In later sections, after examining d i r e c t l y what is contained in a 'machine metaphor', I w i l l undertake a narrative of some landmarks in the present understanding of l i f e from the point of view of the appropriateness of various hypotheses to account for machine-like operations of l i v i n g organisms. contemporary science nor biased by contemporary technology. 33 2.2 MECHANISM, OR MACHINISM? If we r e l y on the main achievements of XVIIth century physiology the narrative of the s c i e n t i f i c revolution as the "mechanization of the world picture" appears deceivingly l i t e r a l . z z Harvey's view of a r t e r i e s , veins and the heart as an hydraulic system with the heart as i t s pump is the outstanding example. Throughout the century many mechanical approaches to the human body's economy with d i f f e r e n t degrees of success can be found. Lorenzo B e l l i n i , d i s c i p l e of B o r e l l i and the leading iatromechanist in It a l y , together with his theory of the kidney as a s i e v e l i k e arrangement to separate urine from blood, advanced a theory of disease r e l a t i n g malfunction mainly to changes in the blood's v e l o c i t y . Descartes's accounts made use of existing or conceivable contrivances of his time as well as chemical technology as sources for models. For instance, in his Treatise of Man he compared digestion with the action of an acid on an a l k a l i , and he alluded to hydraulic machines to account for muscle changes during contraction. The expression coincides with the t i t l e of Dijksterhuis's now c l a s s i c book The Mechanization of the World Picture CDijksterhuis, 1961], where the author claims that t h i s was the f i n a l outcome of the s c i e n t i f i c revolution. However, to focus only on such examples produces a misleading interpretation of what was happening i n t e l l e c t u a l l y during the S c i e n t i f i c Revolution. Descartes's unsuccessful physiological undertakings — he i s not the s t a r t i n g point of any r e a l school of physiology -- in fact i l l u s t r a t e most c l e a r l y the methodological meaning of 'mechanism*. F i r s t l y , in many places Descartes warned the reader about the hypothetical status of the models he uses for p a r t i c u l a r physiological processes. Second, he was not interested in r e j e c t i n g contemporary physiological accounts, as much as in showing that they could be consequences of matter in l o c a l motion. 2 3 For instance, his account of embryological development in his small posthumous t r e a t i s e De l a  formation de 1'animal is remarkably worthless for embryology. If one knew what a l l the parts of the semen of a certain species of animal are, in p a r t i c u l a r , for example, of man, one could deduce from t h i s alone, by reasons e n t i r e l y mathematical and cert a i n , the whole figure and conformation of each of i t s members (as quoted in [Roe, 1981]). Scarcely any statement an embryologist would consider useful can be found in t h i s t r e a t i s e . There is only the general statement that physiological phenomena must be understood as matter and motion alone. Indeed, Cartesian corpuscular ism is the reduction of a l l phenomena to l o c a l motion. Z 3 Thomas S. Hall shows how the physiological explanations or models provided by Decartes in his Traite del homme were contemporarily accepted views re-stated in corpuscular terms [Hall, 1970)]. 35 Robert Boyle also embarked on physiological experimentation. Among others, he devised a lengthy program to research blood [Boyle, 1772] and accomplished many experiments in r e s p i r a t i o n . 2 * However, in our attempt to find the broader meaning of 'mechanism' we can be misled by considering only his mechanico-physiological excursions and not r e l y i n g also on his philosophical writings, such as his Of the Excellency and Grounds  of the Corpuscular or Mechanical Philosophy [Boyle, 1772, Vol. 4]. Here he argues in general terms in favor of the mechanical philosophy against A r i s t o t l e ' s substantial forms and the chymist's "principles and elements". No fewer p r i n c i p l e s than matter and motion are necessary. They are i n t e l l i g i b l e and admit enough v a r i a t i o n to account for the d i v e r s i t y of phenomena we observe. They even allow for the alchemist's dream of the transmutation of metals, a mere rearrangement of compounds!! Evidently for Boyle the "mechanical philosophy" i s an approach in which matter and motion are the only categories necessary for the explanation of natural phenomena. Another outstanding mechanical philosopher, the p o l i t i c a l thinker Thomas Hobbes, discussed the physiology of perception, among Boyle planned an experimentum crucis to decide between his view that the mechanical motion of the lung interacting with the spring of the a i r was the relevant process in r e s p i r a t i o n , and the chemical-particulate view favored by the Oxonians; they were to determine whether i t be the supply of fresh a i r or the motion of the lungs, that keeps animal a l i v e [Frank, 1980]. 36 other things. He did thi s not in the way in which a modern s c i e n t i s t would have, but as part of his agenda to support his p o l i t i c a l conclusions on the foundation of Galileo's law of i n e r t i a and the u n i v e r s a l i t y of motion. In the f i r s t chapter of Leviathan [Hobbes, 1968] he deals with various parts of the mechanism by which the human body operates. Neither in us that are pressed are [the sensible q u a l i t i e s of objects] anything else but diverse motions (for motion produces nothing but motion) [Hobbes, 1966, Vol I, p. 390)]. Sense, imagination, memory, understanding, dreams, are explained in terms of motions: sense in the sentient can be nothing else but motion in some of the internal parts of the sentient [ i b i d ] . The major declared contention of the mechanical philosophers in physiological matters was not the reduction of the inner workings of animals to machine-like behavior. The contention was that phenomena must be explained as matter in motion. But, how are we to interpret the fact that when t h i s point of view was taken to explain the functioning of l i v i n g organisms i t ended up alluding to clocks, springs, wheels, levers, strings and the like ? When were these sorts of contrivances used to i l l u s t r a t e , and when were they brought in as p o r t r a i t s , of what i s r e a l l y happening in an organism? 37 Against contemporary c r i t i c i s m claiming that the laws of motion could not be v a l i d for small motions, Boyle argued that t h i s kind of false reasoning is sim i l a r as saying that "the laws of mechanics may take place in a town clock, but cannot in a pocket watch" [Boyle, 1772]. Here the analogy is e x p l i c i t l y stated but the s p e c i f i c reference to a clock or a watch i s merely accidental. Any pair of large and small machines could s u f f i c e . In Hobbes1 statements l i k e "What i s the heart but a spring, and the nerves, but so many st r i n g s , and the joint s but so many wheels?" [Hobbes, 1968, p. 81], the analogies appear to be not mere analogies. The heart is_ a spring. F i n a l l y , Haller's mechanical theory of n u t r i t i o n as replacement of corpuscles in those parts of the body worn by f r i c t i o n [Holmes, 1975] looks l i k e a l i t e r a l account of what is happening, not an analogy at a l l . Thus, a whole range of degrees of l i t e r a l i t y for the use of 'mechanism' can be found in the writings of the thinkers belonging to the period. Of course, neither the heavens nor animals are l i t e r a l l y clock-works. Fontanelle was r i g h t : Do you say that beasts are machines just as watches are? Put a male dog-machine and a female dog-machine side by side, and eventually a t h i r d l i t t l e machine would be the r e s u l t , whereas two watches w i l l l i e side by side a l l t h e i r l i v e s without ever producing a t h i r d watch (as quoted in [Roe, 1981]). 38 This is one side of the issue, an argument against the use of contrivances in a l i t e r a l way, claiming that in the mechanical philosophy the term 'mechanical' should be understood only as a methodological attitude, namely, to give explanations in term of matter in motion. But was i t possible for the mechanical philosophers completely to dissociate the idea of 'mechanism' from i t s o r i g i n a l l i t e r a l reference to mechanical contrivances? Can the idea of mechanism be completely divorced from a l l remnants of machinism? A careful look at some assertions of Boyle in his defense of the mechanical philosophy w i l l uncover an often overlooked assumption that in part can be traced in part to a common property of machines in Boyle's own time. In addition to the argument in which he uses an analogy between cathedral clocks and pocket watches, Boyle argues in favor of the u n i v e r s a l i t y of matter and motion in a l i t e r a l way. What could be more l i t e r a l than his claiming that he a c t u a l l y has examples that the laws of mechanics are v a l i d for the elementary corpuscles? Nature is more s k i l l f u l than any human ar t i s a n , he cautioned his readers, but there i s one such artisan of whom "good authors t e l l us [that he has managed to make] a chain of a strange tenderness and lightness, insomuch, that i t s divers l i n k s ... [were] fastened to a f l e a , and could be moved by i t " [Boyle, 1772, Vol IV, p. 71] 39 It is not necessary to dig into any history of craftsmanship in the XVIIth century to find i f the tamed f l e a with i t s fa n t a s t i c chain existed. We only have to point out that Boyle insisted on continuity between the microscopic and the macroscopic. The smallness of the flea's chain is a picture of the universe of corpuscles. The grounds for i n t e l l i g i b i l i t y of the mechanical philosophy were prec i s e l y that operations among corpuscles were the same operations seen in the everyday experience — and in mechanical contrivances p a r t i c u l a r l y -- of s o l i d s and l i q u i d s pushing s o l i d s by contact of parts. The big difference between the 'chymist's' active p r i n c i p l e s and the mechanical philosophy is that the l a t t e r r e l i e d on a phenomenon that Boyle and other mechanists considered required no explanation: hard corpuscles transmitting their motion to hard corpuscles. "No motion i s generated but by a body contiguous and moved". Pressure on the outermost part of the organ " i s propagated through a l l the parts of the organs to the innermost" [Hobbes, 1966]. Action through 'hard contact' caught also the imagination of the short l i v e d mechanical chemistry during the l a s t years of the XVIIth century. Nicolas Lemery, author of the very i n f l u e n t i a l Cours de chimie published in 1675, states the s u p e r i o r i t y of 40 mechanical explanations by way of the explanation of p r e c i p i t a t i o n . To say merely that by the conjunction of these two s p i r i t s the aqua f o r t i s is compelled to abandon the metal that i t had dissolved, i s nothing at a l l to the clearing of the question, unless a man w i l l needs give an i n t e l l i g e n c e to these s p i r i t s . Wherefore we must s t i l l have recourse to the agitation and j o s t l e s , for the true reason (as quoted in [Westfall, 1971]) Acids are composed of pointed p a r t i c l e s ("acid points"), a view that could explain not only the action of acid but also the existence of saturation e f f e c t s , which would appear when a l l the points are in use. Microscopical points, micro-saws and the l i k e , acting as macroscopical objects do, provide an i n t e l l i g i b l e explanation in comparison with the obscure i n t e l l i g e n c e of 'active p r i n c i p l e s ' , only, I repeat, i f the interaction of hard corpuscles i s regarded as unproblematic. No wonder that Newton's forces between p a r t i c l e s not in contact were so d i f f i c u l t for the mechanical philosophers to swallow. They st r i v e d -- as Newton had st r i v e d also, unsuccessfully -- to find a 'mechanical' account of gravity. Newton was driven to reject their unquestioned assumption of repulsive contact of hard p a r t i c l e s and, with l a t e r Newtonians, offered an account of p a r t i c l e interactions in terms of attractions and repulsions, e s p e c i a l l y to account for chemical properties. Newton gives a 41 f u l l account of his reasoning in the famous Query 31 to the Qptiks (published in 1705): The parts of a l l homogeneal hard Bodies which f u l l y touch one another, s t i c k together very strongly. And for explaining how t h i s may be some have invented hooked Atoms, which is begging the Question; and others t e l l us that Bodies are glued together by rest, that i s , by an occult Quality, or rather by nothing; and others, that they s t i c k together by conspiring Motions, that i s , by r e l a t i v e rest among themselves. I had rather infer from th e i r Cohesion that t h e i r P a r t i c l e s a t t r a c t one another by some Force (Newton, ... p. 389]. There are ... Agents in Nature able to make the Pa r t i c l e s of Bodies s t i c k together by very strong at t r a c t i o n s . And i t i s the Business of experimental Philosophy to find them out (Ibid, p. 394). When therefore s p i r i t of s a l t precipitates s i l v e r out of Aqua F o r t i s i s i t not done by at t r a c t i n g and mixing with the Aqua F o r t i s , and not at t r a c t i n g , or perhaps  r e p e l l i n g s i l v e r ? . . . Salt of v i t r i o l dissolves homogeneously in water, as i f receding from each other... (Ibid, 387, my emphasis) As in algebra ... in mechanicks, where at t r a c t i o n ceases there a repulsive virtue ought to suceed. It i s remarkable that Newton rejected the appeal to hooks and the l i k e not because he considered such explanations as f l i g h t s of the imagination, but because these kinds of explanations "beg the question". Not only what holds the parts of the hooks together, but what makes them r i g i d ? Although he did not abandon the convenience of r e f e r r i n g to hard corpuscles to account for impenetrability, c l e a r l y he rejects the macroscopic action of sol i d s against s o l i d s as a f u l l account of chemical events. 42 Newton's "principles of s o c i a b i l i t y " , as he c a l l e d these powers of a t t r a c t i o n and repulsion elsewhere, and his r e f u l s a l to formulate hypotheses to explain g r a v i t a t i o n a l , e l e c t r i c a l or magnetic forces — "How these attractions may be performed I do not here consider, What I c a l l Attraction may be performed by impulse or by some other means unknown to me" (Ibid, p. 376) — gave way, after his death, to d i f f e r i n g interpretations of what the t r u l y Newtonian method was. In one way or another, however, a l l the followers of Newton saw themselves as mechanists. One strand considered that the correct Newtonian approach was the extensive use of mathematics to account for natural phenomena. As a consequence for t h i s strand the mechanical philosophy was realized through Newton-style mathematical manipulation of natural phenomena. Actually, i t s advocates — Giovanni B o r e l l i and Stephen Hales, for instance -- accomplished l i t t l e more than a mathematization of contrivance models in a period when mathematization in technical matters was not an extended practice. 3 : 8 5 Another strand i s those who imitated Newton's refusal 3se* See: F r i e d r i c h Klemm: A History of Western Technology [Klemm, 1964] Technological development continued during most of the f i r s t part of XVIIIth century quite separately from the advancement in the science of mechanics. Klemm quotes a relevant l e t t e r addressed by Frederick the Great to V o l t a i r e : "The English have b u i l t ships with the most advantageous section in Newton's opinion, but their admirals have assured me that these ships did not s a i l nearly as well as those b u i l t according to the rules of experience. I wanted to make a fountain in my garden. Euler calculated the output of the wheels which should have raised the water into a reservoir, from which i t was to flow again through canals and again mount on high in the fountains at Sans Souci. My l i f t i n g - g e a r was carried out according to mathematical 43 to feign pointless hypotheses in favor of achieving more limited experimental conclusions. An outstanding member of t h i s group was the highly respected XVIIIth century physiologist Albrecht von Haller. Haller's main contribution to physiology i s seen to be his d i s t i n c t i o n between ' i r r i t a b i l i t y ' and ' s e n s i b i l i t y ' : I c a l l that part of the human body i r r i t a b l e , which becomes shorter upon being touched... I c a l l that a sensible part of the human body, which upon being touched transmits the impression of i t to the soul... (as quoted in [Roe, 1984]). He considers i r r i t a b i l i t y a property "of the animal gluten in the muscular f i b e r . . . to which... i t i s unnecessary to assign any cause, just as no probable cause of at t r a c t i o n or gravity is assigned to matter" ( i b i d . ) . Haller himself claimed that his method was Newtonian, a remarkable fact considering that he worked in German-speaking c o u n t r i e s . z s His 'mechanism' was not exactly that of the calculations but could not raise a drop of water to f i f t y paces from the reservoir. Vanity of va n i t i e s ! Vanity of mathematics!." 2 6 A careful assessment of Haller's methodological views as well as how he was influenced by Newtonianism can be found in Shirley A. Roe's 'The Newtonian physiology of Albrecht von Haller' (Roe, 1984], Here she states: "In my opinion, Haller consciously sought to emulate the Newtonian program in his s c i e n t i f i c work and to construct, in p a r t i c u l a r , a new physiology based upon the canons of the new philosophy". 44 mechanical philosophers, as he added the Newtonian concept of force. Whoever writes physiology ... must explain the inner movements of the animal body, the functions of the organs, the changes of the f l u i d s , and the forces through which l i f e is sustained (Haller: Elementa  physiologiae. as quoted in [Roe, 1984]). But i r r i t a b i l i t y does not require explanation. I r r i t a b i l i t y " i s a physical cause, hidden in the intimate f a b r i c , and discovered through experiments, which are evidence enough for demonstrating i t s existence, [but] which are too coarse to investigate further i t s cause in the f a b r i c " ( i b i d . ) . It appears that the assigning of v i t a l properties to fibers without any further explanation required played an i n f l u e n t i a l role in the waning of mechanism during the XVIIIth century and was a part of the reawakening of v i t a l i s m . 2 " The staunchest advocate of mechanism was J u l i a n Orffay de La Mettrie. He stated as conclusion of his Man a Machine that "man is a machine and that in the whole universe there is but a single substance d i f f e r e n t l y modified" [La Mettrie, p. 148]. In a r r i v i n g at t h i s conclusion he included possible analogies for explaining physiological events, such as X 7~ The waning of mechanism in England in the XVIII i s a well documented fact. "One of the most s t r i k i n g features of English physiology was the dramatic decline of v a r i e t i e s of mechanism and the rapid r i s e of preeminence of alternate v a r i e t i e s of v i t a l i s m " [Brown, 1974]. 45 a v i o l i n s t r i n g or a harpsichord key vibrates and gives forth sound, so the cerebral f i b r e s , struck by waves of sound are stimulated to render or repeat the words that s t r i k e them ( i b i d ) . He also unavoidily took into his discussion the technical c a p a b i l i t i e s of his time, as in the following passage: Even i f man alone had received a share of natural law, would he be any less a machine for that? A few more wheels, a few more springs than in the most perfect animals... (ibid., p. 128). A more s t r i k i n g example of the mechanist as a machinist could scarcely be found. Although i t was a methodological stand t r y i n g to move away from i t s origins in metaphors with mechanical contrivances, mechanism in fact declined when they had exhausted the speculative capacity of models taken from everyday processes and contemporary technology. Some years l a t e r , e l e c t r i c a l phenomena and contrivances enriched again the p o s s i b i l i t y for speculative conjecture about physiological events. But t h i s corresponds to a period that I am not going to deal with in t h i s s t u d y . z s Du Bois-Reymond launched his research a c t i v i t y on the p o s s i b i l i t i e s opened by e l e c t r i c i t y , an endeavor that, notwithstanding some successes, proved to be quite d i f f i c u l t . The f i r s t volume of his Untersuchunaen uber thierische E l e k t r i c i t a t , appeared in 1848. Twenty-five years separate the f i r s t and second parts of the second volume, and in the second Du Bois-Reymond wrote: "So I have at least decided, with heavy heart, to stop 46 2.3 MACHINES In the l a s t section I reviewed some episodes during the S c i e n t i f i c Revolution in which the machine metaphor was brought in as an explanatory device or as a speculative instrument. I w i l l attempt now to characterize the machine i t s e l f , i . e . . what in the f i r s t chapter I c a l l e d the ' l i t e r a l realm'. There are three d i s t i n c t i v e features of a machine: 1) The contrivance i t s e l f , that i s , the hardware. 2) The purposeful character associated with an a r t i f a c t that i s designed with a p a r t i c u l a r objective by a machinist. 3) The implied internal harmony in i t s operation i f any pa r t i c u l a r machine is going to do the task for which i t was designed. The Contrivance where I might just as well have done more than a quarter-century ago...." (as quoted in [Cranefield, 1957]. 47 * The e f f e c t of the running of a machine i s some kind of macroscopic motion of a s o l i d or a f l u i d (usually constrained) in 3-dimensional space, in other words, a change in the geometrical configuration in the environment. The machine i t s e l f is moving and can be described as an arrangement of parts in space. Generally a complicated machine can be analyzed in a combination of elementary mechanisms. z g We can reserve the term machine to the more or less complex arrangements of parts, and these w i l l prompt the analogy with everyday's tools and utensils (hammer and containers, for example) as parts of machines. * To be properly c a l l e d a machine, a contrivance must be able to work in some sort of cycle: i t must be able to operate again and again, almost unchanged after each cycle. Upon f i n i s h i n g a cycle the machine preserves i t s structure, which means i t s parts and the geometrical r e l a t i o n between i t s parts. This feature enables us to highlight an important difference between 'machines' and 'processes'. In the l a t t e r , the features of having parts and working in cycles are out of place. An analogy between organisms and p l a i n 'physico-chemical processes' a s This d i s t i n c t i o n was suggested by Reuleaux, who by the end of XlXth century made the f i r s t systematizatIon of the mechanical contrivance. He distinguished inside the machine d i f f e r e n t mechanisms. The d i s t i n c t i o n is used, for example, by Georges Canguilhem tCanguilhem, 1965] f a l l s too short to be considered as the only feature of a machine metaphor, because i t sets aside central features of a machine such as i t s preservation after the process. At the end of a cycle the machine i t s e l f i s e s s e n t i a l l y in the same configuration as at the beginning. This feature allows us to analyze i t s operation balancing input and output and disregarding the machine i t s e l f . Devices designed to transform one form of energy into another - transductors - are at the center of many thermodynamical arguments. * The composition (that i s , the 'chemistry') of the moving parts in a machine i s responsible for i t s bulk properties, l i k e density and ' s t i f f n e s s ' (encompassing e l a s t i c properties of springs, mechanical c h a r a c t e r i s t i c s of strings as opposed to bars, etc.) , but t h e i r r ole in the general functioning can be accounted for mostly by the parts* p r o f i l e . 3 0 This can be seen when the machine metaphor is carried into the l i v i n g realm in the suggestion that processes inside organisms can be explained in terms of " l i t t l e b i t s of s t u f f pushing each other about" [Woodger, 1929], and into molecular biochemistry as the s t e r i c factor approach. This i s one of the senses in which i t is said that the r e l a t i o n between the parts in a machine i s external. 3 0 The fact that some machines, l i k e the hydraulic press of the steam machine, includes gases or l i q u i d s w i l l not a l t e r in any essential way the features discussed here. 49 * In handiwork manufacturing 'power' i s intermingled with the manipulation i t s e l f . In i t s e a r l i e r versions, some modern machinery began to separate them by t r a n s f e r r i n g power to foot-pedals, and the machinery developed during the Industrial Revolution continued t h i s track. Most, i f not a l l , modern machines have a 'power stage' geometrically or conceptually apart from the manipulating stage, a separation whose importance grew side by side with the advent of energy as a commodity and the ascension of energy as a central concept in science, as well as the view of food as combustible. Purposefulness The h i s t o r i c a l account given in the f i r s t section of t h i s chapter focused on the 'hardware' aspect of the machine. Notable features were l e f t aside in that approach: a machine i s a man-designed contrivance whose parts, movements and composition can be explained making reference to the outcome obtained from them; transmission belts are 'explained' by transmission needs and th e i r detailed structure depends on selected combinations of force/displacement; gears, s t r i n g s , valves, are accounted for by r e f e r r i n g to t h e i r role in the contrivance, to the designer's rationale for including them, to their function towards the f u l f i l l m e n t of a purpose. Nobody w i l l dare to r e j e c t explanations of a machine using t h i s d u a l i t y function and purpose. 50 This d u a l i t y has always been present in b i o l o g i c a l thinking, and i t i s quite e x p l i c i t in the t r a d i t i o n a l view of nature that the s c i e n t i f i c revolution pretended to overcome. In Descartes's animal-machine the apparent problems a r i s i n g from t h i s aspect of the metaphor were solved by appealing to God as the supreme designer. Machine and Harmony Above I referred to the contrivance as a s p a t i a l arrangement of parts. Now I add time. The machine works 'in tune' over time: i t can be considered as an exemplar for harmony, a fact that reminds us that cosmological visions placed the clockwork instead of the heavens as the exemplar of harmony in the XVIIth and XVIIIth centuries. At i t s more basic l e v e l , harmony refers in the case of a machine to an ordered succession of steps. The description just presented displays such a broad view of machine-based metaphors i t would seem that physiological thinking could exist outside i t . The discussion below points out some negative analogies. 51 Machines made of springs, cogs, wheels, gears, chains, s t r i n g s , comply f a i r l y well with the features explained above. Now, the permanence of the structure in machines is at the base of a clear cut separation between structure and process. But p a r t i c u l a r l y in l i v i n g systems we can conceive processes which create meta-stable structures — d i s s i p a t i v e structures in contrast with the more evident equilibrium structure -- themselves becoming the structure for other processes. That i s , processes creating and re-creating structures. In fact, a l l the 'machinery' responsible for processes in l i v i n g organisms are more or less l a b i l e structures whose molecules are continuously renewed, structures which are then outcomes of other processes, structures that sooner or later w i l l disappear. To imagine in physiological studies these l a b i l e structures as fixed, or as quasipermanent structures, may be regarded as an approximation -- a theorist w i l l say that i t i s the dismissal of some term in a d i f f e r e n t i a l equation due to the fact that i t s c o e f f i c i e n t is quite small for the times involved — but i s also a remnant of the machine metaphor. 3 1 Do we not r i s k missing something important about l i f e i f we take Claude Bernard's assertion -- " a l l phenomena which 3 1 In 1929 F.G. Donnan advanced his own conclusions and speculations from A.V. H i l l ' s experimental results working with non-medullated nerve c e l l s and muscle: "the organized structure of these c e l l s is a chemodvnamic structure, which requires oxygen, and therefore oxidation, to preserve i t . The organization, the molecular st r u c t u r e , i s always tending to run down, to approach biochemical chaos and disorganization... The l i f e machine i s therefore t o t a l l y unlike our ordinary mechanical machines... Personaly I believe that ... for the f i r s t time in the history of science we begin ... to understand the difference between l i f e and death..." [Donnan, 1929]. make their appearance in a l i v i n g being obey the same laws as those outside i t " — as an i n v i t a t i o n to study the relat i o n s h i p between structure and function as i f the former is fixed to execute the l a t t e r , imposing the machine metaphor? This l a s t question throws more l i g h t on the point I am trying to stress: the structure in the 'physiological machine* — when portrayed as one enduring the process after a cycle -- is t i g h t l y related to the idea that the structure i s there again, ready to repeat the process. The technical a r t i f a c t , indeed, is designed to serve some end, and i t s structure i s the means to achieve that end. In contrast, the process in the organic 'machinery' might have to be conceived as necessary to preserve the structure i t s e l f , a v i s i o n that would make more i n t e l l i g i b l e the fact that b i o l o g i c a l structures disappear when physiological processes stop. The operations connected with ' l i v i n g ' are the requisites for remaining a l i v e . As organisms, we are not a l i v e in order to enjoy eating; we must eat to be a l i v e . As human beings, up to now we are free to dispute t h i s point either with a physiologist, a psychologist or our parents. In physiological thinking energy i s treated, in some instances, in a clear machine-laden view, as a pre-requisite for a process to occur, in the sense of 'necessary f u e l ' . This i s a description of phenomena carried into science from the analysis of combustibles in machines, where some kind of externality between 53 the power stage and the manipulation stage applies (see below). That i s , in physiology, some energy reactions are often thought of as suppliers of energy in order to accomplish such or such processes. To r e a l i z e that a metaphorical transfer of meaning i s present here i t is necessary to show that t h i s i s not the only way in which we can see the process. An idea from Szent-Gyorgyi might be the best example since i t i l l u s t r a t e s both t h i s point about energy as well as the previous one about fixed structures. The flow of electrons in the respiratory chain is a very de l i c a t e mechanism, and the enzymes responsible for i t must be in very close and precise r e l a t i o n . In Szent-Gyorgyi 1s words, "to interact in a chain, these p r e c i s e l y b u i l t molecules must f i t together most precisely, as the cogwheels of a Swiss watch do" [Szent-Giorgyi, 1969]. For him there was only one way of making i n t e l l i g i b l e how thi s precise mechanism could appear as a resu l t of evolution — the electrons flowing down along the respiratory chain must also be involved in maintaining the s t a b i l i t y of the structure along which they run; t h e i r flux preserves the structure. The electrons flow not l i k e water in a pipe, but l i k e water in a r i v e r , so the waterfall i s where the water f a l l s . The flow of electrons i s not just producing chemical energy to be f i n a l l y stored in those adequate energy-carrying molecules — l i k e ATP -- needed to drive energy-requiring processes. It might 54 be needed to preserve and regulate the structure along which they flow. ATP i t s e l f i s there not only as stored f u e l , but i t s concentration is c r u c i a l for the d i r e c t i o n in which some reactions may go. Fuel i s external in l i t e r a l machines, l i k e the gas engine, but i t i s very u n l i k e l y the case in l i v i n g organisms. Therefore there are some negative analogies of the machine metaphor. These need to be understood h i s t o r i c a l l y . That they are now disanalogies do no preclude the p o s s i b i l i t y of later becoming positive analogies by technological innovation. Improvements of man-made contrivances may come to resemble features found in l i v i n g organisms which are not present in any contemporary devices. Technology has not yet produced r e p l i c a t i n g watches to refute Fontanelle with a Popperian counterexample, but nowadays s e l f r e p l i c a t i n g molecules can be assembled and studied inside a biochemist's r e t o r t . Thinking machines were incredible fantasies in past centuries, but now more than one computer s c i e n t i s t and more than one cognitive psychologist claim that they are here, on our desks: that computers are not l i k e us, but that we are l i k e computers. In fact, philosophers of technology and anthropologists have long been involved in discussion about what comes f i r s t , machines as material expressions of what man sees in himself, or man making himself in the image of the machines he produces. 55 Having examined the l i t e r a l meaning of 'the machine' and some of i t s metaphorical analogies and disanalogles, I w i l l now discuss the development of some central physiological ideas during the XlXth century in l i g h t of the machine metaphor. 2.3 HOT POTS, HEAT MACHINES AND CHEMICAL MACHINES According to the characterization of the machine developed above, there is more to c a l l i n g the animal body a chemical machine than the mere recognition of the fact that chemical processes take place in i t s i n t e r i o r . Aside from the d e t a i l s of the research program launched with the suggestion of the l i v i n g r etort -- how par t i c u l a r organs accomplish the operations assigned through an input-output chemical analysis, or how b i o l o g i c a l r e p l i c a t i o n could be chemically explained, and so on -- other obvious general issues should be addressed, such as: What drives the processes in a pa r t i c u l a r direction? How is harmony guaranteed? Here I w i l l deal mainly with the broad features that would j u s t i f y the use of the term 'machine' as a c o n t r i v a n c e . 3 2 Are organs, c e l l s or c e l l u l a r organelles kinds of physical compartments where chemical processes are going on as i f they 3 2 It appears that i t i s simply the complexity of processes inside a l i v i n g organism discovered by modern research that has made the problem of harmony a major, maybe the major, concern. Is i t just a coincidence that t h i s concern arose pr e c i s e l y when the modern archetype for a machine became the cybernetic one? 56 were in a test tube? Are there s p e c i f i c organs se l e c t i n g some substances to react in t h i s 'test tube 1 while the organs themselves remain intact (or are gradually worn out)? Or, should the structure of any organ, c e l l or organelle be pictured as chemically active, such that the machine is i t s e l f l i t e r a l l y consumed, or not? 2.3.1 LAVOISIER AND LIEBIG: THE HOT POT The modern strand of thinking in terms of chemical machines can be considered as s t a r t i n g from the work of Lavoisier and Laplace which developed the analogy between r e s p i r a t i o n and combustion. According to their interpretation of the results of their renowned ice-calorimeter experiments, oxygen i s used in the body to burn slowly carbon and hydrogen compounds present in the blood forming water and carbonic acid, which reaction takes place in the lungs. The released heat is then spread out through the body by the blood. Although their theory was a huge breakthrough in accounting for animal heat -- i t s e l f a focal point in the debate about the nature of l i v i n g things — p h y s i o l o g i c a l l y i t was weak. The high temperature gradients which could be expected in the body, p a r t i c u l a r l y in the lungs, were not dwelt on by Lavoisier. But Adair Crawford in B r i t a i n explained the absence of perceptible differences in the temperature of the blood before entering and just leaving the lungs by suggesting that there is a difference between the s p e c i f i c heats of a r t e r i a l and venous blood. On the other hand, the additional 'latent' heat taken by a r t e r i a l blood, according to Crawford, i s delivered to the tissues and the blood again regains the s p e c i f i c heat of venous blood, accounting also for the absence of a temperature gradient in the tissues. There are many features in common between Lavoisier's, Crawford's and Joseph Black's theories of animal heat, but chief among them there i s the quite remarkable feature that animal heat did not need to be explained. It could be integrated into the animal's harmony in various ways — for example, pointing out the advantages of having a constant and r e l a t i v e l y high temperature for chemical reactions to occur — but r e s p i r a t i o n was taken to be a physiological event whose d i r e c t aim was only to preserve a constant, r e l a t i v e l y high temperature. Heat exchange was the only important issue. The heat developed by t h i s combustion i s transferred to the blood which passes through the lungs, and thence is transmitted throughout the animal system. Thus the a i r we breathe serves two purposes equally necessary for our preservation: i t removes from the blood the base of fixed a i r . . . ; and the heat which t h i s combination releases in the lungs replaces the constant loss of heat into the atmosphere" (A. Lavoisier, as quoted in [Goodfield, I960]) The analogy between re s p i r a t i o n and combustion i s , then, more than a chemical analogy: i t is also an analogy with a hot pot. 58 The f i r s t general picture of the human body as a chemical machine was an outcome of Justus Liebig's researches, or better, proposals. But, to evaluate Liebig's views, we have to review current research that was going on about the chemical composition of plant and animal tissues. Methods to determine the elementary constitution of organic substances began to appear by the end of XVIIIth century --pa r t l y as a resu l t of the order brought by Lavoisier's theories, experimental results and techniques -- and were f a i r l y well developed by Gay-Lussac in the period 1810-1830. But another way of analysis was also pursued: the treatment of organic substances with milder methods than those revealing elementary composition. These methods could render what later Chevreul c a l l e d "immediate p r i n c i p l e s " [Fruton, 1972, p. 91] from which a c l a s s i f i c a t i o n using some shared chemical or physical properties could also be achieved. For example, coagulation of egg white, curdling of milk and c l o t t i n g of blood were seen as similar processes. The substances r e s u l t i n g from these coagulations were termed albumin, casein and f i b r i n respectively and were included in the same category: "albuminous" substances. Aside from the property of suffering some kind of coagulation, they had one thing also in common from the point of view of elementary constituents: analysis revealed that a l l of them contained nitrogen. 59 Magendie in 1816 k i l l e d several dogs and cats by excluding from the i r d i e t a l l these nitrogen-containing substances, feeding them only sugars and f a t s . This fact, along with their widespread presence in l i v i n g tissues, gave way to the increasingly popular view that these albuminous substances occupy a central role in l i v i n g processes. They were the core of l i f e . The results of uniting both strands, elementary analysis and the immediate p r i n c i p l e s , spurred the imagination of more than one researcher. After the v e r i f i c a t i o n that most organic f l u i d s and tissues were composed mainly of carbon, hydrogen, oxygen and nitrogen, the suggestion arose to base a taxonomy of tissues on variations in their r e l a t i v e presence in those tissues. Highly i n s p i r i n g for Liebig and for later versions of his 'animal chemistry' were the re s u l t s obtained by the Dutch chemist Gerardus Johannes Mulder during the years 1838-9. Mulder claimed to have found some s t r i k i n g resemblances in the elementary chemical composition of animal and plant tissues. Although they d i f f e r e d in the content of sulfur and phosphorus, they appeared remarkably similar in the proportion of carbon, hydrogen, oxygen and nitrogen. From these re s u l t s he inferred that these tissues 60 were formed by some kind of aggregation of a common " r a d i c a l " . 3 3 Following B e r z e l i u s 1 suggestion Mulder c a l l e d i t "protein": The word protein that I propose to you for the organic oxide of f i b r i n and albumin, I would wish to derive from proteios. because i t appears to be the primitive or p r i n c i p a l substance of animal n u t r i t i o n that plants prepare for the herbivores, and which the l a t t e r then furnish to the carnivores" (as quoted in [Fruton, 1972, p. 96) Mulder found an empirical formula for the 'protein' r a d i c a l -C4oHs2Ni O 0 i 2 - and claimed that combinations of d i f f e r e n t numbers of these r a d i c a l s with phosphorus and sulfur accounted for the differences in composition between th i s or that animal or plant t i s s u e . L i e b i g did not follow Mulder completely — in fact, he repudiated the protein r a d i c a l by 1846 -- but his general picture of the body's workings were well in l i n e with the pattern of thought of a chemistry dominated by an interest in the study of n u t r i t i v e requirements. After making considerable improvements in 3 3 By t h i s time organic chemistry was being further developed by leading chemists such as Berzelius, Liebig and Dumas as the chemistry of compound r a d i c a l s , in d i s t i n c t i o n to inorganic chemistry whose aim was to investigate the chemistry of simple r a d i c a l s , where a " r a d i c a l " i s understood to be a simple or complex aggregate of chemical atoms. This is a good place to notice how variable a chemical-machine view of l i v i n g beings and processes must have been in a conceptual environment as giddy as chemistry was. In a period of 50 years, challenging new ideas were suggested by workers l i k e Dalton, Avogadro, Cannizaro, Berzelius, Faraday, Thomsen, Van't Hoff, Kekule, and th e i r opponents. Every few years came a new proposal which altered or challenged a l l that had been held before. 61 the methods of analysis he had learned under Gay-Lussac in France, Liebig with his students in the laboratory at Giessen undertook the task of determining the precise composition of foodstuffs, animal tissues and f l u i d s , and excreta. By 1842, in the Preface of his epoch-making Animal Chemistry, or Organic  Chemistry in i t s Application to Physiology and Pathology [Liebig, 1843] (published both in German and in English in 1842), Liebig presented his chemical tenet: every physical and mental action of an animal is the re s u l t of chemical changes occurring within i t s structure or substance" [Liebig, 1843].^ He dismisses many p o s s i b i l i t i e s here, as he i s taking the ri s k of claiming that he could explain how a hammer works by i t s chemical changes during hammering! I don't know i f at some time in his long s c i e n t i f i c l i f e Liebig had to tackle any objection along t h i s l i n e . On the other hand, to say that Liebig inferred "the physiological role of the various organs from the chemical properties of the elements which made up th e i r substance", as June Goodfield does [Goodfield, 1960], is not, in my opinion, an accurate view of his chemical project. His research was not what later came to be c a l l e d physiological chemistry, but animal chemistry, well centered in conclusions obtained from elementary analysis. With his nutrition-laden view, he was explaining chemically the evident chemical changes undergone by substances in the organism. This pa r t i c u l a r chemical way of dealing with physiological questions was popular enough to generate comments among i t s c r i t i c s l i k e the one related on several occasions by Szent-Gyorgyi (and attributed by him to e a r l i e r V i c t o r i a n s c i e n t i s t s , probably Tyndall): "If you would ask a chemist to find out for you what an e l e c t r i c motor i s and does, the f i r s t thing he would do is to dissolve i t in hydrochloric acid" [Szent Gyorgyi, 1962]. Liebig had a chemical formula for fl e s h (C^sNHsgOio)/ which is l i k e having a chemical formula for e l e c t r i c motors; In 1864, Oskar L i e b r i c h , Professor of Pharmacology at the University of B e r l i n , suggested, along the same l i n e , that 'protagon' — C t i e H 2 ^ i N A P 0 2 z — comprised the main part of 'cerebral matter'(Noel). 62 The book offered a coherent picture -- a l b e i t strongly-conjectural, to say the least — of physiological processes in chemical terms. It contains three parts and two appendixes. The f i r s t part, without a t i t l e of i t s own, deals with questions of heat and n u t r i t i o n a l requirements. The second part is e n t i t l e d "The metamorphosis of tissues" and deals extensively with the b i l e ' s composition and i t s role in the animal economy. The t h i r d part, with no t i t l e , deals with 'motion' and Liebig's highly controversial " l i v i n g force". Liebig stipulated that carbohydrates and fats do not enter into the formation of animal tissues; they are only for combustion. Protein r a d i c a l s transported by the blood to d i f f e r e n t parts of the body are assimilated by the tissues, in whose i n t e r i o r no synthesis i s accomplished, only growth tGoodfield, 1960, p.119]. In the muscles, however, the tissues suffer 'metamorphosis' during exercise, as a r e s u l t of which d i f f e r e n t nitrogen compounds appear, p a r t i c u l a r l y urea, that are later excreted in the urine. The carbon compounds remaining after t h i s process are brought by blood to the l i v e r and converted there to "choleic acid" — according to Liebig, the main component of the b i l e — and returned to the digestive t r a c t to be oxidized in the c a p i l l a r i e s just l i k e other carbon-hydrogen compounds (fats, sugar, starch and gum). Depending on the demands for heat, more or less of these oxidative processes take place, the excess carbohydrates being excreted. 63 This i s , in short, the general scheme under which Liebig suggested that chemical changes occur in the organism. Two main categories of chemical changes occur in the human body in Liebig's view: those generating heat to replenish heat losses, and those related to tissue metamorphosis. Liebig thus agrees with Magendie's r e s u l t that sugars and fats cannot sustain l i f e , although Liebig added his own conception that the human body i s not able to synthesize the protein r a d i c a l and that only carbohydrates and fats are burnt in re s p i r a t i o n . As for this process of burning, Lie b i g remarks: To make use of a familiar but not on that account a less just i l l u s t r a t i o n , the animal body acts, in t h i s respect, as a furnace, which we supply by f u e l . . . In order to keep up in the furnace a constant temperature we must vary the supply of fuel according to the external temperature... [Liebig, 1843, p. 21] Liebig, as I interpret him, is not only accounting for the animal heat in chemical terms — his e x p l i c i t aim in t h i s passage — but is also pointing out, as Lavoisier and others had done before, that oxidation of foodstuffs (more precisely, carbohydrates) i s accomplished in the organism for the sake of heating i t . In whatever way carbon may combine with oxygen the act of combination cannot take place without the disengagement of heat. It i s a matter of indifference whether the combination take place r a p i d l y or slowly, at a high or at a low temperature; the amount of heat liberated is a constant quantity [Liebig, 1843, 29] 64 Liebig's indifference to intermediary steps expresses f i r s t his adherence to a sort of conservation of heat. 3 , 3 Secondly, i t reveals also his understanding that the intermediary steps might be irrelevant p h y s i o l o g i c a l l y -- after a l l , the process is just combustion. With respect to combustion, then, Lie b i g repeats Lavoisier's theme: the furnace. Claude Bernard's d i s s a t i s f a c t i o n with Lavoisier's description of res p i r a t i o n as combustion focused on th i s point. Maintaining that the process i s going on in the blood i t s e l f , either in the c a p i l l a r i e s of the lungs or tissues, as Liebig had contended, is l i k e seeing i t as a combustion process — chemicals are degraded only for the sake of heat. But th i s is not exactly the case, said Bernard. Bernard showed that homeothermy i s a complex regulatory mechanism that in some circumstances is quite d i f f e r e n t from This i s not a version of what later became known as Hess's Law, but a commonly held mistake prior to the general acceptance of the conservation of energy. We now know, f i r s t , that the heat "disengaged" (a word which suggests the c a l o r i c view of heat) when carbon reacts with oxygen i s not i n d i f f e r e n t to the conditions of the reaction ( r e c a l l the differences between Q„ and Q v). Secondly, the heat evolved i s not i n d i f f e r e n t to the chemical environment. For example, consider the independent evaluation of Lavoisier's theory by Dulong and Despretz in 1823 and 1824. They considered the heat evolved by combustion of carbon in foodstuffs as equal to that evolved by combustion of carbon when only carbon i s present in the sample. Later Helmholtz corrected their error, which f i n a l l y explained the discrepancies between combustion of pure carbon and hydrogen with combustion of foodstuffs in an organism. 65 r a i s i n g or decreasing the amount of oxidation. Not chemical combustion, but "physiological combustion". In Bernard's words: But with t h i s important modification to the theory of Lavoisier [that combustion occurs in the tissues not in the lungs] ought we to say that there i s a d i r e c t combustion in the organism and must we conclude that in the general c a p i l l a r i e s for example, the oxygen brought there by the a r t e r i a l blood d i r e c t l y burns the carbon and hydrogen of the blood or the tissues, so that carbonic acid and water are formed, at the same time producing the r i s e in temperature which is a result of t h i s combustion? 1 (as quoted in [Goodfield, 1960, p. 131] To make my point clear I rephrase: for Bernard foodstuffs are degraded in the body's tissues. The process of degradation may be part of many chains of physiological phenomena, but in any case, as a res u l t heat appears. Complex physiological mechanisms, well apart from the degradation i t s e l f , preserve a constant temperature. Thus, chemical reactions in which carbohydrates pa r t i c i p a t e are not 'mere combustion' in spite of the fact that there is an evolution of heat. 2.3.2 HEAT MACHINES, HOT SPOTS AND CHEMICAL MACHINES The discussion of Liebig's second category of chemical processes — tissue metamorphosis — w i l l be centered more on his treatment of muscle contraction and ensuing developments, than on his theory of n u t r i t i o n . But, instead of chasing through the labyrinthine debates between the sponsors of countless 66 hypotheses, I w i l l examine the general way in which mechanical effects were thought to be produced in the muscle by analyzing in some d e t a i l some of the more popular models. Muscle, with i t s remarkable a b i l i t y for macroscopic movement, i s the prototype of a l i v i n g machine — machina carnis, as Dorothy Needham e n t i t l e d her book [Needham, 1972]. Consequently the discussion can help us to grasp what kind of mechanisms or machinisms those researchers were inclined to accept in a l i v i n g being. During the years Liebig conceived his chemical theories, he occupied a t r a n s i t i o n a l position between the c a l o r i c view of heat and the more encompassing p r i n c i p l e of conservation of energy. 3 a His intermediate position allows us to understand why Liebig i s sometimes considered as a forerunner of the p r i n c i p l e of conservation, and sometimes as the v i t a l i s t against whom Helmholtz performed his experiments on muscle. In Liebig's Animal  Chemistry we can find statements l i k e : The want of a just conception of force and e f f e c t , and of the connection of natural phenomena, has led chemists to attribute a part of the heat generated in the animal body to the action of the nervous system. If t h i s view exclude chemical action, or changes in the arrangement of the elementary p a r t i c l e s , as a condition of nervous agency, i t means nothing else than to derive = > s It was mentioned above how the c a l o r i c theory seemed i m p l i c i t in some of Liebig's assertions. But he has statements in his Animal Chemistry where he openly embraces heat as motion: "Let us remember that the most distinguished authorities in physics consider the phenomenon of heat as phenomena of motion" [Liebig, 1843, p. 32], which he then t r i e s to prove with arguments similar to Rumford's. 67 the presence of motion, the from nothing. But no force, [Liebig, 1843, p. 29]. manifestation of a force, no power, come from nothing along with statements about of his idea of " l i v i n g force" l i k e t h i s : The v i t a l force in a l i v i n g animal tissue appears as a cause of growth in the mass, and of resistance to those external agencies which tends to a l t e r the form, structure and composition of the substance of the tissue in which the v i t a l energy resides... [Liebig, 1843, p. 196]. By means of the nerves a l l parts of the body, a l l the limbs, receive the moving force which i s indispensable to t h e i r function, to change of place, to the production of mechanical e f f e c t s . Where nerves are not found, motion does not occur [Liebig, 1843, p. 219]. Never is found in his book any idea that the heat evolved in combustion i s the source of the "force" or "power of motion" for mechanical action in the muscle. In fact, we find again and again e x p l i c i t statements distinguishing chemical processes for the sake of generating heat alone from tissue metamorphosis, the chemical process he associates with the mechanical ef f e c t in the muscles. The sum of the mechanical forces produced in a given time is equal to the sum of forces necessary, during the same time, to produce the voluntary and involuntary motions... The amount of azotised [nitrogen-containing] food necessary to restore the equilibrium waste and supply is d i r e c t l y proportional to the amount of tissue metamorphosed. The amount of l i v i n g matter, which in  the body loses the condition of l i f e i s , at equal  temperatures, d i r e c t l y proportional to the mechanical 68 effects produced in a given time. The amount of tissue metamorphosed in a given time may be measured by the quantity of nitrogen in the urine" (as quoted in [Needham, 1972 J, p. 35; my emphasis). During exercise the tissue is degraded. 'Burnt' would not be the appropriate word to describe what Liebig had in mind, as w i l l be confirmed below by Liebig's further assertions about the process, but no description of any kind of machinery is present anywhere in his Animal Chemistry. Chemically, he affirms, f l e s h i s degraded mainly into choleic acid and ammonium urate, and the presence of urea in the urine can be used as a measure of muscle degradation. To what extent in 1842 Liebig proposed an idea that muscle degradation provides 'force' for the muscle is not clear, and i t i s c e r t a i n l y not clear in what i s said in the underlined portion of the quotation above. As can be seen, i t i s not possible to address the problem of muscle contraction during t h i s period without giving some consideration to the emerging concept of energy and i t s conservation. On the other hand, in the complex conceptual environment leading to our present view of energy the precise chemical events in muscular contraction could not be ignored. This w i l l become even more clear with Helmholtz's work on muscle. In 1845, Hermann von Helmholtz, who had just finished his doctorate under the prestigious physiologist Johannes Muller, published his f i r s t paper on muscle where he showed that indeed 69 a chemical transformation occurs upon contraction. 3 7' It is important to stress here that Liebig had had no d i r e c t proof of t h i s ; after a l l , he was a chemist, not a physiologist. But Helmholtz could not deduce from his experiment either the exact nature of the chemical change or even i f a breakdown of the muscle fiber occurs. Thus, he ended his a r t i c l e promising future work which supposedly was going to include "more exact analysis of the material extracts". This never appeared. In fact, Helmholtz abandoned muscle research after his 1847-8 papers described here. In his next paper on muscle Helmholtz reported careful measurements of temperature changes in muscle after strong tetanic c o n t r a c t i o n s . 3 3 Helmholtz concluded that detectable 3 7 1 Hehlmholtz's f i r s t a r t i c l e on muscle was 'Uber den Stoffverbrauch bei der Muskelaction 1 and was published in the Archiv fur Anatomie und Phvsiologie in 1845. The description of the experiments, as well as some quotations from the a r t i c l e s I have taken from Timothy Lenoir's book [Lenoir, 19821. 3 1 3 'Uber die Warmeentwickelung bei der Muskleaction" i s Helmholtz's second a r t i c l e on muscle. Although published in 1848, i t was presented to DuBois Raymond's newly established Physikalische Gesellschaft in B e r l i n the year before. Lenoir's description of the experiment reported in t h i s a r t i c l e refers to careful measurements of heat production, but in that description we do not see any provisions made to perform actual measurements of heat. Also according to Lenoir, Helmholtz "had shown unequivocally that heat i s generated d i r e c t l y in the muscle tissue i t s e l f and that i t s origins are due to chemical processes in the muscles" [Lenoir, 1982, p. 209]. Lenoir's evaluation i s unobjectionable as far as he is meaning that some heat is produced in the muscle. But i f Helmholtz's aim was to show that Liebig was wrong in the view that heat i s generated mainly by oxidation processes taking place in the blood, his proof f a l l s short of being unequivocal. 70-temperature changes are produced on contraction and that no s i g n i f i c a n t temperature change can be attributed to the nerve. From this l a t t e r r e s u l t he can state for sure that something is wrong with Liebig's claim about the role of nerve action. In the same year 1847, Helmholtz wrote his famous paper 'liber der Erhaltung der Kraft'. A l l u s i o n to the muscle i s r e s t r i c t e d to some few lines in a paragraph: Animals... consume a certain quantity of chemical tensions, and generate in their place heat and mechanical force. As the l a t t e r compared with the quantity of heat represents but a small quantity of work, the question of the conservation of force i s reduced to t h i s , whether the combustion and metamorphosis of the substances which serve as nutriment generate a quantity of heat equal to that given out by animals" (as quoted in [Elkana, 1974]) No doubt mechanical action as a consequence of chemical changes in the muscle was conceptually very relevant for Helmholtz's thinking about conservation of 'force', but i t is remarkable that from the quantitative point of view the work performed by muscles was just ignored. To get a fe e l i n g of the further development of ideas about muscular contraction i t is necessary to keep in mind the interconnections between four strands of research: 71 (1) H i s t o l o g i c a l studies r e s u l t i n g from improvements in microscopy, which by the end of the century had produced results to allow claims, a l b e i t disputed, about the muscle morphology in gross terms resembling accepted views today: the existence of longitudinal fibers in voluntary muscle with alternating anisotropic and i s o t r o p i c bands; the existence of a functional unit of contraction, named "sarcomere" since then, a portion of f i b r e limited by two l i n e s at i t s longitudinal ends (today's Z lines) approaching each other during contraction, with d i f f e r e n t shortenings in the A bands and I bands. (2) Chemical research, some in the old animal chemistry s t y l e of studying chemical composition which had i d e n t i f i e d , for example, the existence of the protein myosin in the muscle t i s s u e . 3 9 But more relevant were the results coming out of the new physiological chemistry, for example, Bernard's results on glycogen 'fermentation' to l a c t i c acid in the muscles. 3 9 As remarked above, proteins were considered the chemical substances responsible for l i v i n g processes, which often meant that they were thought to comprise the structure of c e l l s . The highly 'destructive te s t s ' proper to the techniques of animal chemistry — "Frog muscles were freed from blood by i n j e c t i o n of 1% s a l t solution, then removed and frozen; after 3 hours the mass was cut up and pounded to a snow; on thawing i t gave a syrupy l i q u i d which was f i l t e r e d through a linen c l o t h . . . " [Fruton, 1972] — amply j u s t i f y Bichat's complaints about th i s type of investigation even at the beginning of the century: "one analyzes urine, s a l i v a , b i l e , etc. taken haphazardly from t h i s or that subject, and from their study emerges animal chemistry: so be i t , but that i s not physiological chemistry, i t i s , i f I may say so. the post-mortem anatomy of f l u i d s " (X. Bichat, as quoted in [Fruton, 1972]). 72 (3) Proper 'physiological* experiments with intact animals or with excised muscles subjected to never-ending variations of conditions (fixed ends, one end r a i s i n g d i f f e r e n t loads while s t a r t i n g with d i f f e r e n t lengths, stimuli varying in duration, int e n s i t y and frequency, and so on). (4) Advances in physical and chemical theories that provided the source of possible models, regulated by the concurrently developing thermodynamics and physical-chemistry, a l l in a period when explanations of chemical a f f i n i t i e s and the structure of molecules were frequently changing and quite speculative. The f i r s t model for the conversion of chemical energy into work formulated c l e a r l y within the context of the conservation of energy was probably J.R. Mayer's: Whilst the f i b e r s bend, and the muscle, without suf f e r i n g an a l t e r a t i o n in volume, shortens, work is produced to greater or smaller degree; at the same time in the c a p i l l a r i e s of the muscles an oxidation process takes place to which a heat production corresponds; of th i s heat with the action of the muscle a part becomes •latent' or expended, and t h i s consumption i s proportional to the work performance... The muscle, to speak in familiar terminology, uses heat in status  nascens in performing work" (Mayer, J. R., "Die organische Bewegung in ihren Zusammenhang mit dem Stoffwechsel", 1845 [Qstwalds Klassiker der exakten  Wissenschaften 180), as quoted in [Needham, 1972, p. 39] ) . Mayer's model for the muscle i s , unquestionably, a heat machine, although imprecisely formulated: there are no considerations of 73 the temperatures of heat sources and sinks, no discussion about e f f i c i e n c y . The model of muscle as a heat machine enjoyed mixed acceptance for 50 years, but was almost forgotten by the turn of the century. Adolf Fick strongly c r i t i c i z e d i t (at f i r s t in 1882) on the grounds of the second law of thermodynamics: i f the muscle i s a heat machine, i t must work between two heat reservoirs at d i f f e r e n t temperatures, and a measured 20% e f f i c i e n c y was unthinkable with temperature differences of the order of 0.001 °C detected in the muscle. Ludimar Hermann rejected Mayer's model "on the score that there was not a single fact to be adduced in i t s support" [Macallum, 1 9 1 3 ] , B u t , i n t e r e s t i n g l y enough, even by 1895 the heat-machine theory for muscle contraction had strong advocates, such as Th. W. Engelmann. Engelmann, who had published remarkable papers on microscopical studies of muscle between 1873 and 1895, suggested in the Croonian Lecture before the Royal Society on 1895 [Engelmann, 1895J that Mayer's proposal appropriately modified was more probable than those hypotheses he ca l l e d "chemiodynamic". These he described as "hypotheses according to which contraction of muscle i s a d i r e c t manifestation of chemical a t t r a c t i o n " Ludimar Hermann along with Eduard Pfluger and Max Verworn were leading German physiologists during the la s t decades of the century; a l l of them wrote tr e a t i s e s in physiology widely used in Germany. [Engelmann, 1895]. To dispute Fick's objection to Mayer, i t was only (!) necessary to welcome the existence of very hot p a r t i c l e s in the muscle: we must assume exceedingly large differences of temperature in the stimulated muscle. What holds good of the whole body holds good of the muscle also; the temperature, measured with our instruments, is but an arithmetical average, 'comprising an i n f i n i t e number of d i f f e r e n t temperatures, pertaining to an i n f i n i t e number of d i f f e r e n t points' (Pfluger). From the fact that at the contraction an i n f i n i t e s i m a l part only of the muscular mass i s chemically active, we infer that the temperature of these p a r t i c l e s must, at the moment of combustion, be an uncommonly high one... [Engelmann, 1895]. For an e f f i c i e n c y of 25% he calculates that the temperature of the active p a r t i c l e s would consequently exceed the average temperature of the normal muscle by 100 degrees Celsius, only. The objection that these high temperatures must necessarily destroy the l i f e of the muscle... is of small value only. For i t i s ever an i n f i n i t e s i m a l part only of the muscular mass that is exposed to these high temperatures. At a small distance from these furnaces of heat the temperature must have f a l l e n so low as to be harmless. The muscle w i l l no more be destroyed by stimulation than a steamship w i l l be destroyed by heating the furnaces. The material of combustion only w i l l be destroyed; the vessel as a whole remains unharmed [Engelmann, 1895]. This r i s k y hypothesis of hot spots was supplemented by many arguments and an experimental model. Using the known fact that f i b r i l l a r connective tissue contracts when heated, he 75 experimented with a catgut s t r i n g of a v i o l i n (other features of his model w i l l be treated again below). Variations of what Engelmann had named "chemiodynamical hypotheses" were the subject of many debates. In 1870 Lie b i g advanced a version of these: A l l parts of the animal body arise from inner alte r a t i o n s of protein... in which oxygen has a causal part and one can assume that, i f these products of the protein are sources of energy, the movement which they produce depends, not on th e i r combustion and the  transformation of heat into movement, but on the t e n s i l e force (Spannkraft] (which was pi l e d up in them during t h e i r formation) becoming free on th e i r breakdown (Liebig, 1870, as quoted in [Needham, 1972], emphasis mine). This looks more l i k e a mechano-chemical machine — in t h i s case a machine whose very structure i s considerably altered in the process (supposing that protein somehow gives muscle i t s structure). Liebig was here s t i l l s t i c k i n g to the core of his basic ideas on n u t r i t i o n , among them, that muscle i s degraded during exercise, although t h i s l a t t e r idea was widely questioned by then. Myosin, that protein obtained from muscle press-juice (by Kuhne, in 1859) was, according to Liebig, a product of such degradation; the Spannkraft was restored in the chemical process of rebuilding the l i v i n g tissue, a process made possible, energetically speaking, in part because heat was absorbed. 76 Variations of Liebig's theory of muscular action were proposed to account for the finding that the amount of urea in the urine does not increase accordingly with exercise — u n t i l his death in 1873 Liebig dismissed t h i s r e s u l t — and that in consequence i t i s u n l i k e l y that protein i s i r r e v e r s i b l y degraded during contraction. Fick, Hermann, Pfluger and Verworn were exponents of some of these variations. Hermann, for example, affirms in his Phvsiologie des Menschen that: The muscle contains at any moment a store of a complicated N-containing substance, dissolved in the muscle contents and plasma (which one can designate for sake of brevity the energy-generating or 'inogen' substance) which i s capable of s p l i t t i n g with development of energy; the product of the s p l i t t i n g are, amongst others: COa», s a r c o l a c t i c acid [ l a c t i c a c i d ] , perhaps glycerophosphate and a gelatinous protein body separating out and later contracting firmly (as quoted in [Needham, 1972, p. 37]). Here muscle contraction is explained by means of the contraction of a substance that i s liberated from inogen. The hypothesis proposes to account for chemical events detected in contraction: the evolution of C0 2 during contraction in excised muscles, the fact that a supply of oxygen i s not needed at the moment of contraction, as well as the fact that l a c t i c acid appears after contraction and gradually disappears. As l a c t i c acid was known also to be a product of muscle decay in putrefaction, i t was straightforward to characterize i t as a waste product of the 77 decay of inogen. Later, during the recovery period, l a c t i c acid was reincorporated into the l i v i n g tissue with the help of external oxygen. Protein degradation, or s p l i t t i n g , during exercise was considered not just a process accompanying muscle contraction. In the muscle c e l l and in any other c e l l there i s continuous formation and degradation of a l a b i l e " l i v i n g proteid", and muscle would exhibit a p a r t i c u l a r kind of t h i s v i t a l process. Thus, in 1875 Pfluger wrote:* 1 The l i f e process i s the intramolecular heat of the most highly unstable protein molecule d i s s o c i a t i n g with formation of carbonic acid, water and compounds resembling amides; t h i s protein molecule i s formed in the c e l l substance which continually regenerates i t , and i t grows by polymerization [ s i c ] . As the intramolecular swinging [of the same molecules] changes the a t t r a c t i o n atoms come into r e l a t i o n with one another which otherwise did not work on one another, so one understands the sudden appearance of strong p u l l i n g forces as these atoms at t r a c t each other. If such a t t r a c t i n g parts l i e in an ordered series and i f the a t t r a c t i o n arises at the same moment in the whole s e r i e s , so forces can be generated in this way s i g n i f i c a n t for the muscle twitch (as quoted in [Needham, 1972, p. 38]). Contractile molecules, l i v i n g - l a b i l e proteids, c o n t r a c t i l e networks, a l l represent sorts of chemo-electrical models for "*l 'Beitrage sur Lehre von der Respiration. I. Uber die physiologische Verbrennung in den lebendigen Organismen'. Arch.  f. ges. Physiol.. Vol. 10, 251, 1875. 78 contraction strongly influenced by the concept. 4 2 Arguing for a c o n t r a c t i l e protoplasmic network, Kuhne in 1888 was pleased to remark that t h i s hypothesis "puts back the muscle nearer to protoplasm" (as quoted in [Needham, 1972] p. 140). Verworn, for his part, f e l t some apprehension to talk about a l i v i n g molecule, so he coined the term 'biogen' — and made quite clear the s i m i l a r i t y of muscle contraction with the general process of l i f e : biogen molecules have not in a l l c e l l s exactly the same chemical composition, but ... there are various biogen bodies,... d i f f e r e n t in various d i f f e r e n t i a t i o n s of the same c e l l , such as exoplasm, ... c o n t r a c t i l e f i b e r s , muscle f i b r i l l a e . . . e t c . The biogens, therefore, are the real bearers of l i f e . Their continual decomposition and reformation constitutes the l i f e process, which i s expressed in the manifold v i t a l phenomena [Verworn, 1899]. This was the kind of chemiodynamic model c r i t i z e d — not quite conclusively, in fact -- by Engelmann in his 1895 a r t i c l e . He calculated that only a minute portion of muscular substance was chemically active during contraction, and he found inconceivable "that a r e l a t i v e l y i n f i n i t e s i m a l part of the soft watery substance of the f i b r e " [Engelmann, 1895, p. 415] could set in motion the whole muscle. Later c r i t i c i s m , p a r t i c u l a r l y from F.G Hopkins, would i d e n t i f y the concept of protoplasm as the most t r u l y l a b i l e thing. The new synthetic organic chemistry after Berthelot and Kekule provided the ground to sustain the existence of such giant molecules that physiologists had been advocating. Engelmann's central theme was the presence of ordered birefringent substance in the muscle ("the f i b r i l s are co n t r a c t i l e because they contain doubly r e f r a c t i v e p a r t i c l e s " [Engelmann, 1895, p. 417]). He knew that a l l h i s t o l o g i c a l elements possessing doubly-refractive power tend, even at an ordinary low temperature, to contract... when their volume i s enlarged by the imbibition of a watery f l u i d [Engelmann, 1895, p. 428] He had reported in previous papers that on contraction the anisotropic (birefringent) bands increase in volume while the isot r o p i c ones decrease. Water flowing from the l a t t e r band to the former was a plausible account for contraction. But he himself acknowledged that the same argument he used against the chemiodynamic model — only a minuscule part of the muscle is activated -- could be used against his own 'imbibition model'. That i s why he f o r t i f i e d the l a t t e r with the hypothesis that active thermogenic molecules — hot spots — supplied the fiber with heat to cause contraction. Furthermore, Engelmann pointed out that l a c t i c acid in the medium surrounding the f i b r e — in his experimental model, the birefringent catgut f i b r e -- was able to a l t e r the tension-length properties, so he could provide a rationale for i t s presence in the b i o l o g i c a l system. Engelmann's thermogenic molecules did not receive much attention."* 3 But his imbibition idea was very i n f l u e n t i a l , i f not exactly as he suggested, as an example of how changes of solutions could bring about mechanical changes. Probably the more important among the models inspired by Engelmann were variations of the idea that muscle contraction was caused by changes in surface tension. A model along t h i s l i n e was suggested in the next Croonian Lecture dealing with muscle in 1915 by W. M. Fletcher and F. G. Hopkins [Fletcher and Hopkins, 1917]. They summarized the evidence obtained since 1898 that was eroding the experimental support for inogen: among other things, that C0 3 i s not produced during contraction but during recovery and in consequence the chemical events leading to contraction are not oxidative. The idea of an oxygen-containing substance undergoing some kind of explosion and rendering C0 2, l a c t i c acid and so on was p l a i n l y f a l s e . L a c t i c acid was produced, indeed, but i t could not be interpreted as a waste product: Far from being regarded as a toxic product to be eliminated as rapi d l y as possible... l a c t i c acid [appears to be] an essential agent in the machinery of contraction i t s e l f . The development of acid, with free H-ions, in the neighborhood of c o l l o i d a l f i b r i l s gives the condition for contraction, whether increasing the molecular tension along longitudinal surfaces, or **3 Macallum [Macallum, 1912] quotes a model advanced by N. Zunzt in 1908 requiring spots in the muscle with temperature of 6000 ~C! 81 whether by the process of imbibition [Fletcher and Hopkins, 1917]. It was known that the heat developed during recovery i s much less than i t would be i f a l l l a c t i c acid produced in the contraction were burnt, a fact that was currently interpreted — in part supported by the same authors in previous papers -- that this l a c t i c acid was inserted after oxidative recovery in a precursor. "The l a c t i c acid on that view would be 'part of the machinery and not part of the f u e l ' , to use a familiar Cambridge phrase" they said (ibid./ P- 462). Fletcher and Hopkins then changed their view. The process of recovery must involve the removal of the H-ions that caused the increase in tension, and thi s removal is a change in a physico-chemical system whose potential energy increases. This would account for the missing heat of combustion of l a c t i c acid. 2.4 DISCUSSION OF THE CHEMICAL MACHINE The general problem of any chemical-machine model of the muscle i s , of course, that the chemical energy contained in chemical bonds must be harnessed in some way — t h i s link i s pr e c i s e l y the problem -- to produce a macroscopic mechanical event, contraction, or better, l i f t i n g a weight. One obvious way to accomplish t h i s is by burning substances to obtain heat which is delivered to some arrangement of s o l i d - l i k e structures to produce 82 expansion. 'Obvious' because in the days of the so-called thermodynamical model t h i s method was used extensively in technical contrivances. E l e c t r i c a l machines could have also been ca l l e d upon, but the e l e c t r i c a l models that were advanced were inspired more by th e o r e t i c a l considerations from e l e c t r o s t a t i c attractions or in theories of chemical structure r e l y i n g on e l e c t r o s t a t i c a t t ractions, than by already existing contrivances. Liebig's o r i g i n a l ideas on muscle showed a lack of confidence to postulate a 'something' (energy) whose fate could be used to evaluate quant i t a t i v e l y connections between mechanical effects and chemical changes. He only offered a vague statement about the propo r t i o n a l i t y between the amount of tissue degraded and the mechanical phenomenon, which i t s e l f he did not think of as heat-mediated probably because to him proper combustion in c a p i l l a r i e s was the major process of heat production. His 1870 model, the tension or Spannkraft accumulated after chemical processes, was more a 'why not?' hypothesis than anything else, for there was no evident experimental model. Nor were the inogen or biogen views free from t h i s shortcoming. This is not the case for Engelmann's and subsequent attempts. F i r s t l y they r e l i e d heavily on s t r u c t u r a l observations, notwithstanding how disputable the d e t a i l s were. Secondly, they r e l i e d also on new re s u l t s in physical chemistry. Both directed Engelmann to equate birefringence with c o n t r a c t i l i t y . On the 83 other hand, Fletcher and Hopkins could count on experimental studies on how chemical factors — d i l u t i o n of substances, presence of charged ions and so on -- a f f e c t systems of dispersed p a r t i c l e s or c o l l o i d s in c l e a r l y mechanical ways (such as changes in surface tension or volume). A l l these kinds of models, l i k e heat machines, require a macroscopic geometrical arrangement able to select p a r t i c u l a r degrees of freedom of random-moving p a r t i c l e s to produce a macroscopic effect — loosely speaking, they are machines producing macroscopic order. Interestingly enough, none of them proved v a l i d . The tremendous e f f o r t that went into biochemical investigations of muscle between 1900 and 1930 produced very l i t t l e that has since turned out to be d i r e c t l y relevant to the coupling between chemical and mechanical events [Huxley, 1980, Ch. 2]. Between 1953 and 1957 A. H. Huxley and H. E. Huxley obtained results with the use of electron microscopy and x-ray d i f f r a c t i o n techniques that led to a quite d i f f e r e n t view of muscle contraction: the so-called sliding-filament theory. The theory varied greatly from previous models in the r e l a t i o n between structure and function. But more important than structure and function are the physico-chemical events required to accomplish the s l i d i n g which showed important differences compared to the physico-chemical events posited by models in vogue during the 84 f i r s t decades of the XXth century. It is these l a t t e r differences which are the more relevant to my account. Of course, to i d e n t i f y the level of organization at which the c o n t r a c t i l e mechanism i s located we have to go deeper than the whole organ. The muscle behavior is a sort of summation of the behavior of the muscular c e l l s (also c a l l e d 'muscular f i b r e s ' ) . Each f i b r e i s , in i t s turn, made up of almost i d e n t i c a l longitudinal units, the myofibrils. The myofibrils of a human adult can have a diameter of 50 microns and be as long as the muscle i t s e l f . Along i t s length the myofibril i s made up of a repeating unit, the sarcomere, whose length is approximately 2.5 microns. Figure 1 depicts schematically the sarcomere's structure and the s t r u c t u r a l changes upon contraction. The shortening of the muscle i s not produced by a l t e r a t i o n of the length of the parts of the machine -- not by their contraction -- but by the intercrossing of f i n e l y organized systems of filaments. On the right of Figure 1 a closer view of the filaments is also shown. The a c t i n filament i s a double helix whose threads are formed by the union of many i d e n t i c a l globular proteins of 42kD ca l l e d a c t i n . To grasp the dimensions at stake, each small sphere in the figure w i l l have the same mass as 42000 hydrogen atoms. So, Figure 1 is quite far from discriminating single atoms.'*'* This not the whole story of the thin filaments' composition and workings; in t h i s and the following I r e s t r i c t the description to what i s considered of greater relevance for 85 4 Z.g^-W > F i g . 1 Structure of the sarcomere depicting the s t r u c t u r a l changes upon contraction as well as an s t e r i c view of the thin and thick f ilaments. F i g . 2 Close view at the 'powerstroke' in sk e l e t a l muscle contraction (taken from [Alberts et. a l . , 1989] ). the arguments here presented. 86 The thick filaments are made of ordered bundles of long protein molecules of 510 kD each c a l l e d myosin. Myosin i s a long molecule with two heads at one end. The heads show ATP-ase a c t i v i t y of the i r own: they hydrolyze ATP molecules — the d i r e c t fuel of bioenergetic processes into ADP + P ±. But t h i s enzymatic a c t i v i t y is greatly enhanced when the heads are allowed to bind a c t i n . When s l i d i n g , these heads interact with the actin monomers of the thin filaments. Figure 2 increases the d e t a i l s to i l l u s t r a t e this interaction where the chemical energy i s converted into mechanical energy. The 'powerstroke 1 is produced by a conformational change of the myosin head which displaces the actin filament one actin-length. The new position of the head enhances the release of ADP, completing the cycle. If the other conditions for contraction are present -- for example, adequate concentration of Ca2"" — the head w i l l be ready for another actin-length s l i d e . S t r i c t l y speaking, the way in which chemical energy i s converted to mechanical energy is not dealt with at t h i s level of organization. Without appealing to sub-molecular events, the connection between the release of a phosphate bond and the power stroke i s l e f t as a 'why not?' hypothesis. But a l e v e l of description has been reached in which i t can be assured that the macroscopic event of contraction has been reduced to the sum of microscopical (molecular) mechanical events. These molecular events have the main macroscopic features of the machine, that i s , working cycles and permanence of the p a r t i c i p a t i n g structure. This new account of physico-chemical events, in which the transformation of chemical energy into mechanical energy c a l l s upon microscopic chemico-mechanical transducers, represents the other basic change brought in with the present view of muscle contraction. Changes in fi b e r length or fiber tension in the presence of H-ions, as Fletcher and Hopkins had suggested, are not only d i f f e r e n t models, but very d i f f e r e n t kinds of models. This s i g n i f i c a n t difference, however, should not lead us to ignore an interesting s i m i l a r i t y , namely, that the machine i s preserved during operation in both models. In fact, aside from the d i r e c t experimental evidence, Fletcher and Hopkins included some other considerations showing that their view was sound and coherent with other strands of research about d i f f e r e n t workings of the c e l l . Among these considerations, the following is quite interesting in our search for the basic machine features of the models: With an understanding that the r e l a t i v e l y permanent physico-chemical system of the muscle can, without  i t s e l f undergoing chemical modification, carry changes of potential as a re s u l t of changes in i t s physical configuration, i t becomes easier for us to r e a l i z e that the food-stuffs, or at least that sugar, may be the di r e c t source of the c o n t r a c t i l e energy [Fletcher and Hopkins, 19171. 88 Contrary to the Cambridge phrase they quoted, the separation between fuel and machine i s f u l l y restored. In my inquiry about the features of an alleged chemical machine I have dealt with the muscle as a case study of Liebig's "metamorphosis of tissues" with the muscle the prototype of a l i v i n g machine. Fletcher and Hopkins' discussion of muscle in the 1915 Croonian Lecture was also a case study for the new v i s i o n of chemical events in the c e l l . In a way, theirs was also the general problem of the chemical machine, "the general nature of the processes of metabolism" [Fletcher and Hopkins, 1917, p. 452], of which the muscle i t s e l f was the most s t r i k i n g example. The inogen hypotheses and i t s r e l a t i v e s were general views of the chemical processes inside the 'protoplasm', and although the authors' concern was the production of mechanical effects brought about by chemical changes i t was also, i f not mainly, the general view of chemical events inside the c e l l -- "We are concerned in th i s Lecture in the main with the respiratory oxidative phenomena..." [Fletcher & Hopkins, 1917]. This rel a t i o n s h i p between muscle contraction and the general workings of a c e l l was openly stated. 89 These conceptions of Hermann and Pfluger have had an h i s t o r i c a l importance reaching far beyond the pa r t i c u l a r enquiry into muscular energy. They summarized the only aspects of c e l l metabolism which had received any experimental analysis at a l l , and up to the end of the nineteenth century they not only represented a l l that was known of c e l l r e s p i r a t i o n and of i t s relations to c e l l energy, but they dominated also a l l our ideas of c e l l metabolism in general. It was conceived that the chemical processes of l i f e in a l l c e l l s consisted e s s e n t i a l l y in the building up of elaborate, unstable, and oxygen-charged molecules, by the processes of so-called 'anabolism', into the mystical complexes of i r r i t a b l e protoplasm. From protoplasm, as seen in chemical imagination, a descent by the stages of so-called 'catabolism' was conceived to follow, by which through successive s p l i t t i n g processes energy was discharged, and certain recognizable end-products were displayed [Fletcher and Hopkins, 1917]. Fletcher and Hopkins continue then by quoting Michael Foster, who had been the leading physiologist in England during the l a s t decades of the XlXth century, as follows: The oxygen taken in the muscle, whatever be i t s exact condition immediately upon i t s entrance to the muscular substance, in the phase which has been c a l l e d •intramolecular', sooner or later enters into a combination, or, perhaps we should rather say, enters into a series of combinations. We have previously urged that a l l l i v i n g substance may be regarded as incessantly undergoing changes of a double kind, changes of building up, and changes of breaking down... We cannot as yet trace out the steps taken by the oxygen from the moment i t s l i p s from the blood into the muscular substance to the moment when i t issues united with carbon as carbonic acid. The whole mystery of l i f e l i e s hidden in the story of that progress, and for the present we must be content with simply knowing the beginning and the end (Textbook of Physiology, 6th edition, Book II, p.610) [Fletcher and Hopkins, 1917]. 90 Liebig's metamorphosis of tissues was the predecessor of the chemical picture of protoplasm. The chemical machine that emerged from Hopkins school was remarkably d i f f e r e n t : a chemical structure active through i t s c a t a l y t i c powers. 91 3. THE C A T A L Y T I C MACHINES 3.1 NON-FERMENTATIVE FERMENTS Another kind of chemical machine emerged from a chemical idea foreseen by Jacob Berzelius. In his widely read Jahresbericht (translated to the German by Fr i e d r i c h Wohler, who had stayed a couple of years at Berzelius's laboratory in Stockholm) he reviewed some research results in inorganic chemistry in which the presence of some bodies greatly enhanced a chemical reaction.'* 8 5 To these phenomena Berzelius supplied a name: Constantin Kirchhoff, in 1811, found that in low concentrations a boiled mixture of s u l f u r i c acid with starch produced the change of the l a t t e r into sugar without a l t e r a t i o n 92 It has been shown that many bodies ... possess the property of exerting an influence on complex bodies... causing the rearrangement of the constituents ... without necessarily taking any part therein with th e i r own constituents... I w i l l c a l l i t the ' c a t a l y t i c power'... (as quoted in [Dixon, 1970]). These chemical facts of 'inorganic nature' were referred to in the section on vegetable chemistry [Partington, 1964, p.2631. Berzelius was suggesting that c a t a l y t i c susbtances might be present in other s i t u a t i o n s . When we turn t h i s idea to l i v i n g nature, an e n t i r e l y new l i g h t dawns for us. It gives us good cause to suppose that in l i v i n g plants and animals thousands of c a t a l y t i c processes are taking place between the tissues and the f l u i d s . . . (Berzelius, 1837, as quoted in [Dixon, 1970]). The notion of ' c a t a l y t i c power' offered a speculative instrument that very quickly caught the imagination of the growing c i r c l e of chemists working in l i f e - r e l a t e d phenomena. The mechanical of the acid. In 1833-34 Michael Faraday published the paper 'On the power of metals and other s o l i d s to induce the combination of gaseous bodies', where he extended previous work by Humphry Davy (1817), Louis Jacques Thenard (1823) and others, reporting p a r t i c u l a r l y the s t r i k i n g influence of d i f f e r e n t forms of platinum -- platinum sponge, wire, f o i l , black -- which was known as quite an inert element [Partington, 1964, Ch. 7]. 93 philosophers of the XVIIth and XVIIIth centuries r e l i e d on cogs, wheels, gears, springs and the l i k e to picture l i v i n g organisms as machines. With the progress in chemical knowledge, organs could be thought of as chemically inert bags inside which the reactions of l i f e proceeded, or they could be supposed to undergo continuous degradation — as in Liebig's view of the muscle — and some processes imagined to recover them. But a l i v i n g organism endowed with these ' c a t a l y t i c powers' would be able to take part in guiding the chemical processes necessary to sustain l i f e in such way that after the processes the machine would remain e s s e n t i a l l y intact. What had Berzelius in mind when he proposed to transfer the idea of c a t a l y t i c power to the l i v i n g realm? Fermentation processes, p a r t i c u l a r l y , a l c o h o l i c fermentation. the conversion of sugar into carbonic acid and alcohol, as i t occurs in the process of fermentation cannot be explained by a double decomposition-like chemical reaction between a sugar and so-called ferment, as we name the unsoluble substance under the influence of which the fermentation takes place. This substance may be replaced by f i b r i n , coagulated plant protein, cheese and similar materials, though the a c t i v i t i e s of these substances are at a lower l e v e l . However, of a l l the known reactions in the organic sphere, there is none to which the reaction bears a more s t r i k i n g resemblance than the decomposition of hydrogen peroxide under the influence of platinum, s i l v e r , or f i b r i n , and i t would be quite natural to suppose a similar action in the case of the ferment (Berzelius, 1836, as quoted in (Fruton, 1972, p. 47]). To understand the fate of Berzelius* proposal and the meaning of the modern 'enzyme' we have to trace the history of fermentation. The term 'fermentation' is an ancient word, a victim of many uses. By the end of the XVIIIth and during the XlXth centuries i t remained equivocal, designating sometimes a broad category of processes and sometimes designating s p e c i f i c a l l y some of these processes.*® The following c l a s s i f i c a t i o n can be useful to understand the account presented in t h i s section [Waksman, 1926]: 'digestion' referred to reactions in which organic matter was decomposed by organic juices; 'putrefaction* encompasses those process accompanied by the formation of foul smelling substances and 'fermentation' was r e s t r i c t e d to the situations in which gas — mainly C0 2 — was liberated. The l a t t e r can also be divided into spirituous (wine), acid (vinegar) and putrefactive. On ' c a t a l y t i c force' in organic nature Berzelius was just a commentator, as most of his experimental work was done in inorganic chemistry. The "double decomposition-like chemical reaction" in the quotation above i s an idea due to Lavoisier and Gay-Lussac, who considered fermentation as a chemical process in which a sugar molecule i s s p l i t in two parts, one of each receiving oxygen from the other (in modern notation, what Gay-Lussac f i n a l l y put into the equation was C eH 1 2O e > 2C 2H B0H + 2C0 =). But of course Lavoisier recognized that the ferment was *** The existence of equivocal uses of the word is very far from being h i s t o r i c a l l y i rrelevant, as w i l l be seen later in the b r i e f account of Pasteur's dispute with L i e b i g . 95 necesssary. According to Lavoisier, a small quantity of i t i n i t i a t e s a process that then runs on i t s own. Berzelius agreed in the view that fermentation is a chemical process, but the fact that to be accomplished a small quantity of something c a l l e d a ferment was needed, as well as the fact that the overa l l process can be described chemically by an equation not involving the ferment i t s e l f , was enough for him to make an analogy with inorganic catalysts In spite of the meaningful results reported by the advocates of fermentation as a process related to the l i f e of microorganisms during the years 1836-9 (for example, Schwann, Kutzig and Cagniard-Latour), Berzelius stated in his 1839 Jahresbericht that yeast is "no more to be regarded as an organism than ... a p r e c i p i t a t e of alumina" [Harden, 1911], a position he maintained u n t i l 1848. A chemical approach to fermentation was backed mainly by the more prestigious chemists of the continent, l i k e Liebig and Wohler, although there were important differences in the accounts.'* 3 Liebig published in 1839 a paper explaining his view. He admitted, following Gay-Lussac, that the presence of atmospheric *7' There were contradictory reports about the fate of the ferment: did i t grow, remain the same or disappear during the process? Thenard claimed that ferments l i k e yeast diminished in weight with the process, loosing nitrogen and carbon and that th i s carbon was present in the C0 2 evolving fermentation came from the yeast. •*s At the same time the brewery industry worked with the idea that fermentation is a l i f e - r e l a t e d processes [Harden, 1911]. 96 oxygen was c r u c i a l for the process of fermentation to go. This atmospheric oxygen entered in contact with the nitrogenous substance of the ferment and the l a t t e r became quite unstable, communicating i t s motion to loosely bound sugar molecules which decomposed into alcohol and carbonic acid, while the ferment i t s e l f suffered a l t e r a t i o n . The congruity of t h i s view with the 'metamorphosis of tissues' we described above is remarkable. The chemical view in general, though not the p a r t i c u l a r models, r e l i e d on strong experimental facts: the discovery of soluble ferments. In 1833, Anselme Payen and Jean Persoz obtained from germinating barley a substance they c a l l e d diastase that after being dried was able to convert starch into sugar. Evidently t h i s substance was not a l i v i n g organism, and although t h i s was not the f i r s t report of t h i s sort, i t c e r t a i n l y marks the beginning of a period during which similar important findings of other so-c a l l e d soluble ferments were announced. Schwann, following a current l i n e of research in digestion, reported in 1836 that he had i d e n t i f i e d the active p r i n c i p l e in g a s t r i c juices that were known to dissolve coagulated egg white and gave to i t the name pepsin. He remarked on i t s resemblance with the agents of alc o h o l i c fermentation, as there was "a spontaneous decomposition of organic materials, e l i c i t e d by a substance acting (through contact?) in a minimal quantity" (Schwann, 1836, as quoted in (Fruton, 1972, p. 68]). In 1837 Liebig and Wohler reported about an albuminoid material obtained from almonds -- emulsin they c a l l e d i t -- capable of decomposing amygdalin On the other hand, fermentation as a phenomenon c o r r e l a t i v e with l i f e received strong support with the work of Louis Pasteur. In experiments beginning in 1857 he claimed, among other things, that a microorganism for l a c t i c fermentation indeed existed --i t s non-existence was used as an argument by those who held the opposite view -- and that a simple equation for al c o h o l i c fermentation l i k e Gay-Lussac's could not be true because other chemical susbtances l i k e succinic acid and glycerine are produced as well. Pasteur's experiments during three years culminated in his now c l a s s i c 1860 'Memoire sur la fermentation alcoholique' where he p l a i n l y declares that the chemical act of fermentation is e s s e n t i a l l y a phenomenon c o r r e l a t i v e with a v i t a l act. To circumvent the undeniable existence of soluble ferments Pasteur affirmed that those encompassed by his theory were the "properly so-called fermentations", and about the chemical fate of reactions in the l i v i n g organism he formulated a Newtonian 'hypothesis non f i n g o ' . B O Chemists, or physiological chemists, **9 Ferments in human s a l i v a , pancreas and vegetable tissues were reported one after the other. By the end of the nineteenth century, the number of soluble ferments had grown to two dozen. For a brief although detailed account, see [Fruton, 1972 J. 0 0 It i s remarkable that some modern historians and almost invariably a l l modern authors of text books fond of making h i s t o r i c a l remarks usually j u s t i f y extreme mechanicist positions in this period appealing to an unavoidable crusade against 98 were interested p r e c i s e l y in the chemical events inside the microorganism. In 1858 Moritz Traube warned against stopping just there, at the border of the organism: Even i f a l l decay processes depend upon the presence of infu s o r i a or fungi, a healthy natural science would not permit [Schwann's] hypothesis to preclude further investigation. It would simply conclude from these facts that there are present in microorganisms chemical susbtances which evoke the appearance of decomposition. It would attempt to i s o l a t e these substances and, i f i t could not do so without changing their properties, then i t would only conclude that a l l means used for separation must have exercised a chemical influence on these very substances, changing them. (M. Traube: Theorie der Fermentwirkungen 1858, as quoted in [Sourkes, 1955]; my emphasis) Soluble ferments would be the evident model to r e l y on when thinking about the internal chemical machinery producing fermentation. After a l l , pepsin, for example, and pancreatic ferments, were substances excreted by organisms. Ferments are the causative agents of the most important vital-chemical processes not only in the lower, but also in the higher organisms" (Traube, M. Die chemische Theorie der Ferment wirkungen und der Chemismus der Respiration, Ber. dtsch. chem. Ges. 1877, Vol, 10, a quoted in [Fruton, 1972]) ' l i v i n g forces' and the l i k e . However, Pasteur's predicament that in fermentations and putrefactions microorganisms must be present, for which he i s charged with 'vitalism' — ' v i t a l i s t ' i s anything but a 'neutral descriptor': for a b i o l o g i s t " i t is worst than being blamed as communist by an FBI agent" [Szent Gyorgyi, 1962] -- is never j u s t i f i e d r e c a l l i n g a necessary crusade against would-be Paracelsian heirs not far from claiming, as Paracelsus did, that i t is possible to obtain mice from r o t t i n g organic material inside closed bottles. 99 In fact, Marcelin Berthelot, who had been working in general synthesis of organic compounds with alcohols and sugars, reported in 1859 that he had obtained from yeast a soluble ferment able to invert sugar. And later in his i n f l u e n t i a l Chimie Organique  Fondee sur l a Svnthese published in 1860 he suggested also the a l l pervasive presence of fermentations: among the phenomena that are related to the transformations of matter in l i v i n g beings, whether during the l i f e or t h e i r death, there are few that do not involve fermentations to a greater or lesser degree (as quoted in [Fruton, 1972, p. 52]). The idea of fermentation, the "mysterious ... change which converted the i n s i p i d juice of the grape into stimulating wine" [Waksman, 1926], was beginning to be used not just as the process producing vinegar, wine or l a c t i c acid in milk. More than 'fermentation', Berthelot seems to be suggesting a 'fermentation-l i k e chemical process', that i s , c a t a l y s i s . Thus, Anselm Payen wrote under the entry "Fermentation (chemistry)" in the Encyclopedie du XIXe s i e c l e : One should understand by t h i s word a spontaneous reaction, a chemical a l t e r a t i o n excited within a mass of organic matter by the sole presence of another substance, without the l a t t e r borrowing or lending anything to the body i t decomposes... (as quoted in [Laszlo, 1986, p. 430]). 100 In 1878 Willy Kuhne designed a term supposed to avoid equivocal arguments about the nature of fermentation processes. Instead of the ferments of fermentation (which are chemical substances, also c a l l e d 'unorganized ferments') and the ferments of 'properly so-ca l l e d fermentations' (which are organisms, also c a l l e d •organized ferments'), Kuhne proposed to c a l l the unorganized ones 'enzymes' ('in zyme', that i s , inside yeast). Although he in s i s t e d that the new term is not intended to imply any pa r t i c u l a r hypothesis, but i t merely states that in zyme something occurs that exerts this or that a c t i v i t y , which is considered to belong to the class c a l l e d fermentative (as quoted in [Fruton, 1972, p. 74]). But his new word ended up being used to imply that t h i s something is a 'substance', a soluble ferment. This was F e l i x Hoppe-Seyler's idea -- the generalization of enzymes as internal soluble ferments d r i v i n g a l l chemical phenomena as hydration and dehydration reactions [Kohler, 1964] -- although very u n l i k e l y Kuhne's, who was one of the contributors of the protoplasm theory. Hoppe-Seyler's was in general the same idea as the one behind Traube's 'causative agents' quoted above. The controversy on the nature of fermentation — whose effects are s t i l l f e l t today -- is a well documented story and we are not going here into many of i t s d e t a i l s . Some current historiography describes i t as the debate between a ' v i t a l i s t ' approach 101 (Schwann, Pasteur) and a 'mechanist' approach (Liebig, Berthelot, Traube, Hoppe-Seyler), that i s , not a debate about fermentation, but one about the scope of chemical research in organic processes. Actually, the polemic was not devoid of the common exercise of d i s q u a l i f y i n g the opponent's ' s c i e n t i f i c i t y ' , and even included angry nationalism exacerbated by the Franco-Prussian c o n f l i c t . Patriotism was brought in by Pasteur against those Frenchmen defending a "German theory". The so-called v i t a l i s t s of t h i s polemic are sometimes blamed for imagining insurmountable barriers to the true chemical approach for entering the c e l l and unraveling i t s secrets, which is supposed to be in general what Traube and Hoppe-Seyler had in mind: internal enzymes. 3 1 But we have to r e f r a i n from thinking that the present 'enzyme theory of l i f e processes' was the only chemical approach that 'Homo s c i e n t i f i c u s ' could pursue. = z For almost twenty years u n t i l Edward Buchner's surprising success in obtaining a juice from yeast capable of some alco h o l i c fermentation in 1897, the chemical view of the inner workings of the c e l l was that of the protoplasm, described in the second chapter. It was absolutely r a t i o n a l to deduce from the protoplasm idea that some chemical behavior was not possible when the B 1 Pasteur did not suggest such kind of obstacle. In fact, in the 1880s he t r i e d -- not with great enthusiasm, I guess -- to extract soluble ferments from yeast. s z This i s what, for example, T.L. Sourkes contends: "The history of XlXth century c o n f l i c t between the mechanist and v i t a l i s t outlooks in science may very appropriately be t o l d from the standpoint of enzyme chemistry" (Sourkes, 1955]. i n t e g r i t y of the c e l l is disrupted. In addition, in spite of the subsequent successes of biochemistry, we could have foreseen some shortcomings in Traube's views about internal substances when they were suggested, aside from the fact that soluble ferments, or in the new vocabulary, internal enzymes, had not been obtained. What are the effects of considering that fermentation processes inside the c e l l are accomplished by "substances"? Is i t possible to explain the effect of a hammer as an iron-woodish action? Would we dare to say that a mitochondrion, without whose fine organization important chemical wonders would not ex i s t , i s a 'substance'? From hindsight i t might be said that i t i s not proper to bring in an analogy with a hammer, since i t i s a mechanical process very u n l i k e l y to produce the kind of chemical changes that were to be explained. But Traube's acceptance of chemical changes being produced by mechanical action shows how unstable was the t e r r a i n on which any proposal was standing: The pressing out of the juices is not a mere mechanical, but simultaneously a chemical attack upon the substance of the f r u i t . In the c e l l s , the individual substances are l o c a l i z e d near one another in a d e f i n i t e way, and their mutual action i s another matter than in the juice where they are mixed indiscriminately with one another". (M.Traube: Uber das Verhalten der Alkoholhefe in Sauerstoffgasfrein Medien. Ber. dtsch. chem. Ges.. 1874, Vol. 7, as quoted in [Sourkes, 1955]). In t h i s view i t i s more than expected that chemical phenomena in the c e l l depends not only on the substances r as he stated elsewhere, but in the organization as well. 103 Kuhne's new word was re a d i l y adopted. But the idea of extending 'enzyme' to include the inner chemical behavior of the c e l l turned almost inevitable after Buchner's experiment. Some years after the success was reported, Franz Hofmeister suggested openly the new tenet. We thus arrive at the conception that the c a r r i e r s of chemical processes in the c e l l are c o l l o i d a l c a t a l y s t s , an idea that agrees p e r f e c t l y with other d i r e c t l y demonstrated facts. For what are the ferments of biochemists but c o l l o i d a l catalysts (Franz Hofmeister, Die chemische Organization der Z e l l e f 1901, as quoted in (Kohler, 19721). Berzelius's suggestion about c a t a l y s i s , i f not interpreted as the mere introduction of a word or as a theory about alc o h o l i c fermentation, but rather as a novel source of models about the chemical accomplishments of an harmonious system able to preserve i t s e l f while d i r e c t i n g continuous transformations — a model for a chemically active machine -- was going to have immense success. 3.2 COLLOIDAL MACHINERY In the l a s t section I showed how i t was being r e a l i z e d that alc o h o l i c fermentation was a process produced by substances, that i s , a process chemically definable not only in i t s input and output but also in i t s intermediate steps. We saw also the r i s e 104 of the promising idea that 'ferments' as chemical substances could provide a model for thinking about every chemical process going on inside the c e l l . The meaning attached nowadays to the words enzyme, protein and such may d i s t o r t our perception of the problems at stake. Schwann, for example, did not obtain the enzyme that biochemists c a l l today pepsin. He dried a chemically undefined g a s t r i c juice showing pepsin-like a c t i v i t y . Zymase, what Edward Buchner obtained from yeast, was a juice extract capable of some sort of al c o h o l i c fermentation but with remarkably lesser a c t i v i t y than the o r i g i n a l yeast. Today i t is recognized as a mixture of twelve enzymes and some coenzymes. In 1900 'ferment', or even 'organic ca t a l y s t ' , were concepts defined in terms of their actions as substances whose presence in small amounts a l t e r s the rate of a chemical process without suffering a l t e r a t i o n themselves. So, the idea that the chemical machine acts through agents c a l l e d ferments leaves s t i l l open questions l i k e : What are the chemical compositions, structures and c l a s s i f i c a t i o n of these agents? How do they act? Can they be characterized as chemical individuals? These are the kind of questions whose answers are necessary to validate the characterization of an organism as a chemical machine — not only input-output analysis, but also the means whereby they act. 105 In his f i r s t e dition of Animal Chemistry. Liebig indeed invents chemical reactions when what he a c t u a l l y knows is the elementary chemical composition of reactants and alleged products. With t h i s information, he balanced chemical reactions he had invented by adding or subtracting appropriate amounts of water, oxygen, carbonic acid and ammonia. For example, the reaction 5 atoms of protein + 15 of starch + 112 of water +5 of water giving 9 atoms of choleic acid +9 of urea +3 of ammonia + 60 of carbonic acid was a possible one because the quantities of the constituent atoms, C, H, 0, and N were equal on both sides. This chemical reasoning "from the desk" (as Berzelius in a strong c r i t i q u e c a l l e d i t ) could hardly replace detailed chemical research. Kohlrauch, though a mild c r i t i c of Liebig's book, pointed out that "one could reach the r i d i c u l o u s conclusion that the oxidation of protein in the body produced the poison prussic acid and the explosive compound fulminic acid" (as quoted in [Holmes, 19631). In the t h i r d edition L i e b i g took out the 106 appendix with the equations and began to inquire about the intermediate steps. But researchers did not have to think about the more complex achievements of a l i v i n g being such as protein synthesis to ask challenging questions. Compelling enough was the problem of oxidation. How could oxygen, a rather unreactive substance outside the animal body at low temperatures, becomes so f i e r y inside i t ? In the previous chapter we saw that examples of c a t a l y t i c behavior in inorganic reactions were ci t e d by Berzelius when he proposed to extend the model of c a t a l y s i s to the chemical actions of organic bodies. In many of the examples that were taken from the inorganic realm, the existence of a metallic surface was responsible for the acceleration of a chemical reaction in which atmospheric oxygen participated. These c a t a l y t i c surfaces provided a theme that was not abandoned in speculations about the mechanism of oxidation — and fermentation in general — for many decades. J.R. Mayer, for example, after accepting the view that combustion occurred in the blood, imagined the c a p i l l a r i e s ' walls as porous surfaces able to promote oxidation. The conception of the c e l l as a chemical machine whose reactions were effected by catalysts (many of them probably acting through surfaces), discoveries of the microscopists, developments in 107 thermodynamics, p a r t i c u l a r l y what later was c a l l e d physical chemistry, blended by the turn of the century into a suggestive idea: there is a kind of physico-chemical system whose behavior and composition can account for processes occuring in the c e l l : c o l l o i d s . Colloids held out the promise of chemists, physiologists, h i s t o l o g i s t s and physicists working together in harmony. It is useful to begin by assessing how the nowadays almost extinct phrase ' c o l l o i d a l behavior' caught the imagination of b i o l o g i c a l thinking at the turn of the century. 3.2.1 WILLIAM B. HARDY [T]he u n i f i c a t i o n of the b i o l o g i c a l sciences was begun by the recognition of the c e l l as the unit of a l l l i f e , and of the glutinous sarcode as i t s physical basis... Living matter i s composed of very large molecules, and substances so b u i l t possess certain special properties which mark them off from simpler substances. To them the name of c o l l o i d s is given, after the type of the class the j e l l i e s . . . It is only in the c o l l o i d a l state that we could have within so small a space so great a d i v e r s i t y of matter, and such differences of chemical potential as must exist to support the multifarious a c t i v i t i e s of the l i v i n g c e l l , combined with the molecular mobility necessary to give chemical change free play. On [the] blending of opposites, on the curious combination of i n e r t i a and chemical mobility in the c o l l o i d state, is reared the whole fabr i c of the dynamics of l i v i n g matter [Hardy, 1906, p.447]. So wrote William Bate Hardy (1864-1934) in his "The Physical Basis of L i f e " , a popular a r t i c l e published in 1906. Hardy, a 108 b i o l o g i s t by t r a i n i n g , turned to the c o l l o i d chemistry of proteins (today we would say biophysical chemistry) during the middle of his research l i f e and ended up doing research on lubricants. He is mostly remembered for his discovery of the influence of the a c i d i c or basic character of a solution on the e l e c t r i c charge borne by proteins, a discovery leading him to develop the concept of i s o e l e c t r i c point of a protein. After general statements l i k e those quoted above on the marvels performed by the c o l l o i d a l state of matter, Hardy singled out three features of l i f e -- choice and purpose, growth, and heredity -- to show that physico-chemical systems can behave in ways p e r f e c t l y resembling these. He i l l u s t r a t e s choice and purpose with the phenomena of chemotaxis, "the influence of a chemically heterogeneous medium upon the free c e l l s l i v i n g in i t " [Hardy, 1906, p. 450]. Opalina, a parasite l i v i n g in the frog's intestine, does not simply respond to chemical changes in i t s immediate environment. It displays chemotactical behavior in the presence of concentration gradients, but i t s behavior also depends on the medium in which i t was immersed before. The microorganism manifests a sort of memory. The f a c u l t y ... of storing impressions, so that the response to any par t i c u l a r stimulus is in part conditioned by the stimuli which have preceded i t , i s a familiar property of l i v i n g matter, and also of matter in the c o l l o i d a l state. The molecular state of a j e l l y is not fixed by the conditions of the moment. Just as a piece of wrought iron has properties d i f f e r e n t from those of cast iron, so the circumstances which attend the making of a j e l l y - temperature, concentration, and 109 the l i k e confer on i t an internal structure which controls i t s properties for years to come. Each j e l l y , therefore, has an i n d i v i d u a l i t y due to the record which i t bears of i t s past [Hardy, 1906, p.452]. S 3 Regarding growth, Hardy describes experiments performed with Paramecia in which senile decay after many generations was reversed by " a r t i f i c i a l rejuvenation" after immersing them in infusions of beef extract. Many simple chemical solutions can lead to t h i s a r t i f i c i a l rejuvenation: "Thirty minutes' immersion of an individual Paramecium in very d i l u t e solution of potassium phosphate was found to restore v i t a l i t y " . The s a l t , so he thinks, provides a sort of chemical shock restoring again the necessary difference from the inactive state of equilibrium. Rejuvenation is a puzzling phenomenon, he admits, but there is a physical behavior resembling i t . F i r s t he points out the s t r i k i n g properties of surface layers, where a l l physical properties become abnormal ... when the surface energy forms a large f r a c t i o n of the t o t a l molecular energy, as in films, or f l u i d in fine c a p i l l a r i e s , ordinary chemical or physical knowledge f a i l s us [Hardy, 1906]. And then he continues: Some breath-taking generalizations are braved by Hardy here: "The b i o l o g i s t i s cognizant of no break in the series from the choice of [the bacteria] V i b r i o , which can be analyzed al g e b r a i c a l l y , to the choice of a c h i l d between two toys" [Hardy, 1906, p. 451]. The relationship between 'free w i l l ' and the automatic response of elementary organisms to external stimuli has haunted the mind of many researchers coming from the physical sciences. Jacques Loeb went through similar lines of arguments to Hardy's, and many years later Max Delbruck abandoned his phages to study chemotactical behavior. 110 There is no lack of evidence to prove that the l i f e l i k e c h a r a c t e r i s t i c s of c o l l o i d a l matter, i t s capacity for storing impressions, the elusiveness of i t s chemical and physical states, are due to the fact that an exceptionally large f r a c t i o n of t h i s energy i s in the form of surface energy [Hardy, 1906, p. 57]. F i n a l l y the physico-chemical phenomenon that could account for rejuvenation can be brought forward: [I]t is just in experiments on surface energy that one finds a case analogous to the ef f e c t of the s a l t in bringing about rejuvenescence ...: By the use of minute amounts of s a l t s one can f i x in the surface layers cer t a i n q u a l i t i e s [direction] which for instance define the e l e c t r i c properties of the surface... The s a l t can be removed, the ef f e c t remains. So far as we know, in the absence of active chemical intervention, i t w i l l endure for a l l time, always exerting a d i r e c t i v e influence upon the molecular events in i t s neighborhood. In these experiments there i s , i t seems to me, a re a l clue to the nature of the phenomena of rejuvenescence [Hardy, 1906, p. 457]. As for heredity, Hardy did not refer to c o l l o i d s but r e l i e d on microscopical observation of chromosomes to show that only physico-chemical processes are ocurring. In his use of the concepts of protoplasm and c o l l o i d s Hardy plays here an intermediate position. "Protoplasm" was a term, i f not invented by Thomas Huxley, surely made popular by him in his 1868 lay sermon "On the Physical Basis of L i f e " and " c o l l o i d a l behavior" was surely intended to replace i t , as "protoplasm" was I l l considered too fuzzy. 3"* Thus Hardy's intermediate position, and to grasp the sort of novelty that colloidology promised to bring in to explain the puzzling features of l i f e , some statements from his essay are worth quoting: "Proteids unquestionably are the material basis of l i f e , but when isolated after the death of the c e l l they are not l i v i n g . They are chemically stable bodies... It is therefore conjectured on experimental grounds that the l i v i n g molecule is b u i l t up of proteid molecules, that i t is so complex, so huge, as to include as units of i t s structure even such large molecules as these. But when such very large molecules enter into chemical combination with one another, whether by reason of the great magnitude of the masses of matter in each in r e l a t i o n to the magnitude of the d i r e c t i v e forces, or because the molecules themselves, owing to their great s i z e , to a certain extent cease to be molecules at a l l in the physical sense, and possess the properties of matter in mass, i t i s at any rate cer t a i n that in their chemical combinations they cease to follow the law of d e f i n i t e combining weights which is the basis of chemistry. The quantity of the substance A which w i l l combine with a fixed quantity of the substance B is determined not only by the chemical nature of A and of B, but also by the chance conditions of temperature and concentration of the moment. This class of chemical compound i s within l i m i t s continuously adjustable to changes in i t s surroundings, while at the same time i t r e s i s t s those changes by reason of i t s i n e r t i a . Here is a real adumbration in non-living matter of the chemical flux which is the abiding c h a r a c t e r i s t i c of the matter of l i f e . Hardy explains further: °* At least four rather important essays were written under the t i t l e "The Physical Basis of L i f e " . Aside from those of T.H. Huxley and W.B. Hardy, E.B. Wilson published one in 1923 [Wilson, 1923] and J.D. Bernal another in 1951 [Bernal, 1951]. A sort of general strategy exists in them: there are unanswered questions in inorganic processes that can be as enigmatic as those in the l i v i n g realm as to invent magical virtues in the workings of the l a t t e r ones. But some features proper to l i f e can be imitated by well defined physico-chemical systems. 112 The b i o l o g i s t speaks of these molecular complexes as molecules, and in that he i s wrong in so far as the word implies a defined structure, a chemical unit. The biogen, or chemical unit of l i v i n g matter, i s not a fixed unit l i k e the molecule of dead proteid; i t is an average state. That we know from the chemical phenomena of l i v i n g matter [Hardy, 1906, p. 461]. s a From t h i s a r t i c l e we conclude without hesitation that c o l l o i d s could be taken as di r e c t explanations of r e l a t i v e l y complex achievements of organisms. How did this enthusiasm about the c o l l o i d a l state of matter arise? Not very long before Hardy, Thomas Graham had introduced the concept of c o l l o i d s in his work on d i f f u s i o n . 3.2.2 THOMAS GRAHAM AND THE ORIGINS OF COLLOIDOLOGY. In 1861 Thomas Graham published in the Philosophical Transactions  of the Royal Society an a r t i c l e e n t i t l e d 'Liquid Diffusion applied to Analysis' as part of his researches on d i f f u s i o n rates. There he reported a noticeable difference in some very general physical and chemical properties between a class of substances he ca l l e d " v o l a t i l e s " , r e f e r r i n g to d i f f u s i o n in liq u i d s using an analogy with gases, and those he ca l l e d "fixed". The l a t t e r are "marked out by the absence of the power to a a Hardy c l e a r l y does not mean "molecule" in our sense of the word. Indeed, i t is only with Staudinger's idea of "macromolecule" that the term becomes stable. 113 c r y s t a l i z e " and by their extremely slow d i f f u s i o n . Examples of these are hydrated s i l i c acid, starch, albumen, ge l a t i n , vegetable and animal extractive matters, among others. Although often l a r g e l y soluble in water, they are held in solution by a most feeble force. They appear  s i n g u l a r l y inert in the capacity of acids and bases, and in a l l the ordinary chemical r e l a t i o n s . But, on the other hand, the i r peculiar physical aggregation with  the chemical indifference referred to appears to be  required in substances that can intervene in the  organic processes of l i f e . The p l a s t i c elements of the animal body are ground in this c l a s s . As gelatine appears to be i t s type, i t i s proposed to designate substances of the class as c o l l o i d s , and to speak of their peculiar form of aggregation as the c o l l o i d a l condition of matter [Graham, 1861, my emphasis] Subsequently he adds a passage that has received much attention from hist o r i a n s . Although chemically inert in the ordinary sense, c o l l o i d s possess a compensating a c t i v i t y of their own a r i s i n g out of their physical properties. While the r i g i d i t y of the c r y s t a l l i n e structure shuts out external impressions, the softness of the gelatinous c o l l o i d partakes of f l u i d i t y and enables the c o l l o i d to become a medium for l i q u i d d i f f u s i o n l i k e water i t s e l f . The same pe n e t r a b i l i t y appears to take the form of cementation in such c o l l o i d s as can exist at a high temperature. Hence a wide s e n s i b i l i t y on the part of c o l l o i d s to external agents. Another and eminently c h a r a c t e r i s t i c q u a l i t y of c o l l o i d s is their mutability. Their existence i s a continued metastasis. The c o l l o i d a l i s , in fact, a dynamical state of matter; the c r y s t a l l o i d a l being the s t a t i c a l condition. The c o l l o i d possesses ENERGIA. It may be looked upon as the probable primary source of the force appearing in the phenomena of v i t a l i t y . To the gradual manner in which c o l l o i d a l changes takes place (for they always demand time as an element), may the c h a r a c t e r i s t i c protraction of chemico-organic changes also be referred [Graham, 1861] . 114 What Graham considered appropriate for carrying out organic processes was not, of course, the extremely slow rate of d i f f u s i o n of these c o l l o i d s of animal and vegetal o r i g i n , but their resistance to chemical changes, as well as their capacity of preserving structure and at the same time r e g i s t e r i n g changes after interaction with the environment. Others (Liebig, perhaps) could have seen t h i s sort of chemical i n e r t i a as a shortcoming, but Graham (himself not a b i o l o g i s t or an 'animal chemist') saw this s t a b i l i t y as the very attribute signaling c o l l o i d s as the bearers of l i f e . Graham characterized c o l l o i d s as those substances that did not go through parchment membranes. But apart from his di a l y z e r , an instrument that was going to be used later as one of a set of experimental tests for c o l l o i d s , he did not deal with the re l a t i o n s h i p between c o l l o i d behavior and l i f e processes, at least not in a way that would allow anybody to suspect that 40 years l a t e r his d e f i n i t i o n was going to be considered as a breakthrough in the inquiry about the nature of l i f e . In fact, he suggested the term ' c o l l o i d ' only 8 years before his death, as part of his continued research on chemical separation by mechanical methods, f i r s t pursued with gases. As can be seen in the c o l l e c t i o n of his Chemical and Physical Researches he made only a few more experiments with inorganic c o l l o i d s . Only with hindsight could later b i o l o g i s t s and physiologists r e c a l l Graham's work as the o r i g i n of a school of b i o l o g i c a l thinking. 3.2.3 FROM THOMAS GRAHAM TO WOLFGANG OSTWALD. Wolfgang Ostwald (1886-1943) i s considered the most remarkable propagandizer of c o l l o i d chemistry in i t s beginnings. The son of Wilhelm Ostwald, he was a zoologist by tr a i n i n g , and worked under Loeb in 1904-6 in C a l i f o r n i a . In 1906 the Ko l l o i d Z e i t s c h r i f t was established in Germany, and one year later Wolfgang Ostwald was appointed i t s editor. In 1909 Ostwald established the Kolloidchemische Beihefte. After a series of lectures in the United States Ostwald published The World of Neglected  Dimensions r whose f i r s t German edition was published in 1914 and had undergone ten editions by 1927. In 1909 he published the Grundriss der Kolloidchemie, translated into English as A Handbook of C o l l o i d Chemistry in 1915. Wo. Ostwald acknowledged that in the study of c o l l o i d s themselves no theoreti c a l breakthroughs had occurred from Graham's death u n t i l the beginnings of the 1890's. In the i n t e r v a l , proteins had been recognized as c o l l o i d s due to the j e l l y - l i k e appearance of their solution in water and because they did not passed through most semipermeable membranes. Proteins and inorganic c o l l o i d s — of the l a t t e r probably the more thoroughly analyzed were c o l l o i d a l gold, arsenious sulphide and s i l i c i c acid (Si0 2.nH20) — had 116 other properties in common: they scattered l i g h t (Tyndall effect) and sometimes in the cone formed by the ray of l i g h t traversing the solution very small p a r t i c l e s were seen undergoing Brownian motion. Moreover, the salting-out procedure widely used to p r e c i p i t a t e proteins was equally e f f e c t i v e in p r e c i p i t a t i n g inorganic c o l l o i d s . The new t h e o r e t i c a l insights came after Svante Arrhenius 1 theory of e l e c t r o l y t i c d i s s o c i a t i o n . Harold Pincton (1867-1956) and Samuel Ernest Linder found that c o l l o i d a l p a r t i c l e s were e l e c t r i c a l l y charged and explained the persistence of the c o l l o i d a l solution by e l e c t r i c repulsion between the p a r t i c l e s . The coagulation effects of the salting-out method was the result of adsorption of opposite charged ions appearing after the e l e c t r o l y t i c d i s s o c i a t i o n of a neutral s a l t . Other fi n e r d e t a i l s of the behavior of c o l l o i d s were also r e a d i l y explained by r e f e r r i n g to the e l e c t r i c charge. For example, Schultze's 'valency r u l e ' enunciated in 1882, according to which 'tervalent metal s a l t s * -- later under the d i s s o c i a t i o n theory known to bear three elementary charges in solution — were more ef f e c t i v e as coagulators than bivalent ones, and these more ef f e c t i v e than monovalent [Partington, 1964, Ch. 23]. During the decade 1890-1900 i t was also suggested that the individual p a r t i c l e s wandering in a c o l l o i d a l solution are of 117 mechanical aggregates of various numbers of small chemical molecules, a view that would replace Kekule's proposal in 1877 that these aggregates r e a l l y are molecules with atoms held together by valence forces. And the newly established physical chemistry contributed to the f i e l d not only with the formalism developed by W i l l i a r d Gibbs to tackle systems of coexisting phases, but with e f f e c t i v e methods to treat surface phenomena. The range of alleged applications of c o l l o i d chemistry was impressive: "Industries such as dyeing, cement, rubber, soaps, photography, a r t i f i c i a l t e x t i l e f i b e r s , starches, glass, tanning involved c o l l o i d phenomena" [Oesper, 1945]. Although nowadays some of these f i e l d s surely do not r e l y on the th e o r e t i c a l grounds developed between 1900-1920 (a main concern would emerge in polymer chemistry, b u i l t upon the concept of macromolecule) and although probably these f i e l d s were more empirical than t h e o r e t i c a l l y based, what i s seen in the early 1900's i s the i n s t i t u t i o n a l i z a t i o n of a d i s c i p l i n e whose pract i t i o n e r s promised achievements in many f i e l d s . From Wolfgang Ostwald's handbook [Ostwald, 1919] a r e l i a b l e overview of the f i e l d , i t s research program and predicted applications can be obtained. I d e n t i f i c a t i o n of the C o l l o i d a l State In a chemically heterogeneous l i q u i d we can have either a true solution, a c o l l o i d solution or a coarse mechanical suspension. 118 The l a t t e r can be e a s i l y separated by f i l t r a t i o n or using a hand centrifuge. The f i r s t i s a molecular solution, and we can distinguish i t from the intermediate one because the intermediate, the c o l l o i d solution, gives a positive Tyndall e f f e c t . Once i d e n t i f i e d as a c o l l o i d a l solution, two remarkably d i f f e r e n t behaviors can be observed: the suspension c o l l o i d s -- c a l l e d also suspensoids, lyophobic or hydrophobic, although the terms are not exactly equivalent -- w i l l show low v i s c o s i t y and small molecules w i l l d i f f u s e through them at rates very similar to those of a pure solvent; the emulsion c o l l o i d s -- emulsoid, l y o p h i l i c or hydrophilic -- have a great v i s c o s i t y noticeably affected by temperature changes. Notwithstanding the macroscopic homogeneity of a c o l l o i d a l system i t has at least two d i f f e r e n t phases thermodynamically speaking, one continuous and the other disperse. Fog i s a c o l l o i d in which the disperse phase is a l i q u i d and the continuous one a gas; in a foam the disperse phase is a gas while the continuous one a l i q u i d . We can have gas in s o l i d (lava), s o l i d in gas (smoke), and so on. Nevertheless, the more interesting ones involve a l i q u i d . In a l l these cases the disperse phase can be in d i f f e r e n t 'degrees of dispersion', conferring d i f f e r e n t propertoes on the system. 119 •Equations of State* for C o l l o i d a l Systems The state of a c o l l o i d a l system depends on pressure and temperature l i k e any other system but is remarkably affected by the degree of dispersion, concentration and the e l e c t r o l y t e s in solution. In general the degree of dispersion decreases with increasing concentration, and d i f f e r e n t degrees of dispersion can be obtained with the same concentration depending on the procedures for preparation -- one of the grounds for the statement that c o l l o i d s have 'memory1-- and d i f f e r e n t degrees of dispersion may cause, for example, d i f f e r e n t c o m p r e s s i b i l i t i e s . In a c o l l o i d a l solution there can be d i f f e r e n t p a r t i c l e sizes, so the degree of dispersion can not be described by a single number. Changes in v i s c o s i t y , b o i l i n g and freezing points were commonly analyzed and contrasted with predictions from th e o r e t i c a l models, either to choose between d i f f e r e n t models or to complete parameters inside one of them. = e Most substances when in the disperse phase assume an e l e c t r i c charge, the sign of which was detected, for example, by examining the migration under e l e c t r i c f i e l d s . In t h i s kind of study Hardy discovered in 1899 that in the case of proteins the sign depended s e After his request for the purchase of a centrifuge from Sweden was rejected, Staudinger engaged in a long study of the v i s c o s i t y of ' c o l l o i d a l solutions' that became the grounds for his hypothesis of 'macromolecule' to replace the concept of aggregates. 120 on the degree of a c i d i t y or a l k a l i n i t y of the solution. Coagulation of c o l l o i d solutions can be obtained in d i f f e r e n t ways, but the more interesting way was using the influence of e l e c t r o l y t e s . Suspensoids, that i s , hydrophobic c o l l o i d s when the continuous phase is water, were coagulated by adding small quantities of neutral s a l t s , whereas emulsoids required substantial amounts. With emulsoids i t was found that coagulation was produced by lower concentrations of t r i v a l e n t than bivalent and bivalent than monovalent ions, but also more e f f e c t i v e l y according to the chemical species of the ion in th i s order: Cations: Ba""" > Sr*"*" > Ca"~"" > Mg** Cs* > Rb* > K* > Na* > L i * Anions: SO*- > C l ~ > Br" > N03~ > I - > CNS~ The differences in cations were found to be less marked. The effect was claimed to be almost general, independent of the chemical features of the c o l l o i d involved. These rankings are the so-called lyotropic or Hofmeister series [Partington, 1964, Ch. 23]. Similar or related orders were observed in the influence of these ions on v i s c o s i t y and osmotic pressure. 121 Interestingly enough, the reverse of coagulation was c a l l e d peptization, a term o r i g i n a l l y r e f e r r i n g to the action of pepsin (a p r o t e o l y t i c enzyme) on proteins. Theoretical Framework of the C o l l o i d a l State It was promptly realized after Graham that any c r y s t a l l o i d could be prepared in the form of a c o l l o i d , the more re a d i l y the more complex the substance. Therefore, the c l a s s i f i c a t i o n separating c r y s t a l l o i d s from c o l l o i d s was not tenable. Instead, • c o l l o i d ' began to refer not to a set of substances, but to a state. C o l l o i d i s not a chemical e n t i t y l i k e s a l t , acid, base... but i s expressive of certain physical elements l i k e mechanical heterogeneity... C o l l o i d chemistry deals with the rel a t i o n s of the surface energies to other kinds of energy as shown in an e s p e c i a l l y c h a r a c t e r i s t i c way in dispersed heterogeneous systems. Thus viewed, colloid-chemistry appears as a branch of physical chemistry [Ostwald, 1919, p. 112]. Three ideas formed the core of colloid-science during the years 1900-1920: the e l e c t r o s t a t i c explanations of s t a b i l i t y and coagulation to which we referred above; the idea that " c o l l o i d chemistry i s not the study of c o l l o i d materials but that of the c o l l o i d state of materials" [Ostwald, 1919], a view that i d e n t i f i e d what we c a l l today 'macromolecule' as aggregates of small molecules; and the relevance of surface energy, which put c o l l o i d chemistry in the f i e l d of physical chemistry, in the 122 attempt to explain the behavior of substances in the c o l l o i d state. Jacques Loeb stated quite c l e a r l y the aggregation hypothesis when he described the b a t t l e f i e l d in the h i s t o r i c a l introduction of his i n f l u e n t i a l book Proteins and the Theory of C o l l o i d a l  Behavior: The c o l l o i d a l state i s defined by c o l l o i d chemists as that state of matter in which the ultimate units in solutions are no longer isolated molecules or ions, but aggregates of molecules ...[Loeb, 1924]. As for the t h i r d idea, surface energy, Wolfgang Ostwald was c a t e g o r i c a l : "A development of much surface [sic] is the fundamental property of dispersoid systems" [Ostwald, 1919, p. 66]. The extreme subdivision present in disperse systems brings about an enormous increase in surface area, but what grows even more remarkably is the r a t i o between the absolute surface area of the entire disperse phase to the t o t a l volume of the same, what Ostwald c a l l e d ' s p e c i f i c surface'. Starting subdivision from a cube with edge of 1 cm (and thus 6 cm3 of t o t a l surface area and a s p e c i f i c surface area of 6 cm2) to smaller and equal cubes, Ostwald calculated that we obtain, for example, 10 1 S cubes with edges of 0.1 microns, a t o t a l area of 60 m= and s p e c i f i c surface of 6 x 10°. Evidently, most of the behavior of a system of 10 1 < s cubes w i l l depend on what happens on the interface between the system in the dispersed phase and the continuous phase. Physical 123 chemistry, p a r t i c u l a r l y the thermodynamics of heterogeneous systems developed by Gibbs, offered the t h e o r e t i c a l tool to treat surface phenomena. Three phenomena must be considered: adsorption of molecules on the interface, surface tension, and changes of dens i t y . The consequences of the fact that chemical behavior i s l i k e l y to be determined by what happens in the interface can be far reaching. Since c o l l o i d s belong to the heterogeneous systems, the general law of chemical kinetics governing such systems may be applied to them. This states that the amount of chemical change in the unit of time is proportional to the absolute surface [Ostwald, 1919, p. 93]. We would expect that the phenomenon of c a t a l y s i s would be e s p e c i a l l y marked in c o l l o i d systems. The distinguishing c h a r a c t e r i s t i c of a catalyzer resides in the enormous change which i t is capable of bringing about in the v e l o c i t y of a chemical reaction... [I]t has been shown that many c a t a l y t i c effects may be brought about by highly dispersed surfaces of a l l kinds, and that the e s p e c i a l l y important c a t a l y t i c reactions of the organic ferments may be c l o s e l y imitated by various inorganic materials in the c o l l o i d state, such as the c o l l o i d metals ( i b i d . . p. 94). 3.2.4 PROMISES OF COLLOIDS IN PHYSIOLOGY. Such i s a bird's eye view of the f i e l d of c o l l o i d chemistry as a developing branch of physical chemistry around 1915. Colloids were necessarily alluded to in physiology and physiological 124 chemistry because after extraction proteins behaved as c o l l o i d s . 'Colloids' was a physico-chemical concept. It was not only the r a d i c a l procedures of the late XlXth century physiological chemists in the i r search for the chemical composition of tissues that made them attracted to c o l l o i d s . Cytologists had been suggesting the thesis that apart from differences due to s p e c i a l i z a t i o n , there is something in common inside a l l l i v i n g c e l l s , a ' j e l l y - l i k e ' substance which they ended up terming "protoplasm", and which Max Schulze in 1863 described as "the physical basis of l i f e " [Singer, 1989, p. 342]. Since i t was found that protoplasm showed a positive Tyndall effect and that the p a r t i c l e s responsible for i t wandered in Brownian motion, protoplasm was thought to be in a sort of l i q u i d state. Carl Naegeli discovered that protoplasm contains nitrogen and so i t is a proteid [Singer, 1989, p. 340]. With the use of new staining and f i x a t i o n techniques, microscopists began to inquire about the structure of protoplasm, some of them claiming the existence of network structures in i t , others r e j e c t i n g t h i s . In 1899 W.B. Hardy published an a r t i c l e in the Journal of  Physiology. 'On the Structure of the C e l l Protoplasm' [Hardy, 1899], describing the polemic in the following way: At the present moment the l i v i n g c e l l protoplasm is regarded by many as being composed of two substances, one of which is disposed as a c o n t r a c t i l e net according to some, as a r e l a t i v e l y r i g i d framework according to others, or as free filaments. Other workers again regard c e l l protoplasm as being b u i l t up of a more 125 s o l i d material, and of a more f l u i d material which occupies the minute spaces of vacuoles which are hollowed out un the former. S t i l l others view i t as a homogeneous j e l l y holding granules. L a s t l y there are s t i l l those who deny the truth to a l l these views and maintain that the l i v i n g c e l l protoplasm i s homogeneous in so far that i t does not manifest the r e l a t i v e l y coarse structure which these theories ascribe to i t . Its peculiar and transcendent q u a l i t i e s are according to them associated with molecular and not molar structure [Hardy, 1899, p. 249 J. Hardy's a r t i c l e was to become a landmark in the study of c e l l structure, as he showed there that: The lack of consonance in the views held as to the structure of the c e l l protoplasm is traceable in the main to the fact that they are large l y based on d e t a i l s of structure v i s i b l e both in fresh and fixed c e l l s which are the r e s u l t of the physical changes which the l i v i n g substance undergoes in the act of dyeing, or at the hand of f i x a t i v e s [Hardy, 1899, p. 249]. This he showed mainly by producing in a r t i f i c i a l c o l l o i d systems the same structure that was claimed to exist in protoplasm: A study of the action of reagents upon c o l l o i d a l matter shows that when an insoluble modification i s formed there is a separation of s o l i d p a r t i c l e s which are large molecular aggregates, and that these become linked together to form a comparatively course s o l i d framework having the form of an open net which holds f l u i d in i t s meshes [Hardy, 1899, p. 291]. No cytol o g i s t could anymore think of the structure of protoplasm without r e f e r r i n g to these findings. Even though Hardy had argued i t was an a r t i f a c t , the mesh-like structure did not disappear at 126 a l l from biology-related texts, in part because Hardy's results had two faces. On the one hand, they cast doubt as to the structure claimed to exist in c e l l s before f i x a t i o n and dyeing, but on the other, they stressed the a b i l i t y of c o l l o i d s to form structures through chemical changes, some of them simple chemical or physical a l t e r a t i o n s . It was unavoidable but to accept that any c e l l , p a r t i c u l a r l y under mitosis, experienced s t r u c t u r a l changes l i k e those that can be made to appear in simple c o l l o i d s o l u t i o n s , 9 7 Along with t h i s strand of inquiry about the structure of protoplasm there were also grounds -- and l i k e l y stronger than the merely chemical -- to confer upon c o l l o i d s a central position in the theory of l i f e processes, p a r t i c u l a r l y in the workings of the c e l l . " L i f e as we know i t i s indeed inseparably bound up with matter in the c o l l o i d state", wrote E.B. Wilson in the 1928 edition of his c l a s s i c The C e l l in Development and Heredity 9 7 It is important to stress that c o l l o i d chemistry did not have a unifi e d view about the nature of the s o l i d - l i k e structure appearing after the process of gelation, and so two d i f f e r e n t theories emerged from the microscopist's results about the physico-chemical state of the protoplasm. There was one led by Butschli, maintaining that gelation was the formation of a continuous s o l i d net holding l i q u i d in i t s meshes. But in the tr a n s i t i o n from sol to gel (as thi s process i s called) the rate of d i f f u s i o n of small molecules as well as the e l e c t r i c a l conductivity of the system changes gradually, a result that could not hold after the net i s formed. The other view of the process led by Carl Naegeli held that gelation involved the growing of 'micellae', sorts of aggregates with c r y s t a l l i n e properties, which, by the way, were suggested by Nageli as the responsible for the po l a r i z a t i o n of l i g h t scattered by b i o l o g i c a l tissues. See [Bayliss, 1924]. 127 [Wilson, 1928, p. 633], even though two pages later he gave strong support to Loeb's findings in protein chemistry (see below) that were to be major factors in the replacement of molar mechanisms by molecular ones. Wilson's rationale for his c o l l o i d -view is remarkable: This conception seems l i k e l y to prove as f r u i t f u l in cytology as i t has been in physiology. More modern attempts [than e a r l i e r r e t i c u l a r theories of protoplasmatic structure] to consider the structure and transformations of protoplasm, the mechanism of mitosis, the nature of f e r t i l i z a t i o n , the nature and function of the c e l l membrane and the physiological r e l a t i o n between nucleus and protoplasm, have for the most part taken the c o l l o i d a l nature of protoplasm as a common s t a r t i n g point; and numerous recent observations on both l i v i n g and fixed c e l l s tend to demonstrate that we are here on the right track. On the physiological side of the subject t h i s is even more obvious, and many s t r i k i n g cell-phenomena have in a measure been imitated in a r t i f i c i a l c o l l o i d a l systems: for instance, the properties of surface films or membranes, the antagonistic e f f e c t of inorganic s a l t s on the nature and s t a b i l i t y of the system, or the changes of v i s c o s i t y in the l i v i n g cell-substance [Wilson, 1928, p. 633]. Hardy's r e s u l t s , as referred to by Wilson, increased the degree of apprehension about the results obtained from microscopy, but increased also the confidence that c o l l o i d s and th e i r associated set of concepts were the candidates to provide the explanation for the more complex phenomena of l i v i n g matter. What were, in more d e t a i l , the alleged successes of the c o l l o i d a l view? In the preceding chapter the explanations for muscle contraction r e l y i n g on some sort of surface action -- one of the preferred 128 theoret i c a l tools of colloidology -- were treated in d e t a i l . Other avowed successes can be found in physiology textbooks or in essays written by the propagandists of the c o l l o i d a l approach. William Maddox Bayliss (1860-1924) was one of the most i n f l u e n t i a l advocates of the primacy of the c o l l o i d a l approach. Himself an outstanding researcher in physiology, he i s the author of P r i n c i p l e s of General Physiology (Bayliss, 1924J, a widely used and respected textbook on the subject. 5" 3 In 1923 he published The C o l l o i d a l State in i t s Medical and Physiological  Aspects, [Bayliss, 1923] apparently as an answer to Loeb's 1922 book (see below). Referring to the permeability changes in c e l l membranes — one of the examples brought up by Wilson in the quotation above --Bayliss states that two kinds of systems of two immiscible l i q u i d s are possible..., say, an emulsion of o i l in water or of water in o i l . If we may compare the o i l to land, we may look upon the former system as a number of islands in a large lake; the l a t t e r as a number of small lakes surrounded by land. Fish could pass from one side to the other of the former system; rabbits not. The opposite would be the case with the lakes surrounded by land. A layer of the o i l in water system would only allow to pass through i t substances soluble in water, s e The fourth edition of his book was published in 1924 some days after Bayliss's death, and was prepared by a "Committee of Sir William Bayliss's friends", as A.V. H i l l writes in the preface, "partly in order to ensure that what we regard as the greatest book of t h i s kind s h a l l continue to be available for the service of the s c i e n t i f i c public". 129 because the water is the only continuous phase. The l a t t e r would be permeable only to substances soluble in o i l . . . Clowes shows also that one system can be changed into the other by the action of certain s a l t s , such as those of calcium... [Bayliss, 1923]. Immediately after he warns the reader about the crudeness of the model. In his P r i n c i p l e s he devoted a chapter to this complex issue, stressing that no simple a r t i f i c i a l membrane had been able to reproduce the s e l e c t i v e mechanism combining size and adsorption properties of permeants. The protoplasmatic substance of the c e l l , he wrote, is capable of forming a new membrane on a fresh surface: The substances present in the protoplasm which lower surface energy... w i l l be concentrated at the interface between protoplasm and external phase... In t h i s way the membrane is formed [Bayliss, 1924, p. 144]. Cl o t t i n g of blood is another example, according to Bayliss, of a process that can be handled within colloidology: It i s obvious that the process is e s s e n t i a l l y a change in the physical state of certain c o l l o i d s present in the plasma. An unnecessary degree of complexity has been introduced into the numerous theories of c l o t t i n g by the assumption of a large variety of participants, each supposed to be a d e f i n i t e chemical compound and given a name. There is evidence, indeed, that the investigation of the phenomena with due regard to the c o l l o i d a l factors involved w i l l s i m p l i f y the theories [Bayliss, 1923]. 130 Another phenomenon ascribed to c o l l o i d s was a r t i f i c i a l parthenogenesis, f i r s t obtained by J. Loeb and later pursued by his assistant Wo. Ostwald. With Martin Fischer, Ostwald published some research a r t i c l e s in which f e r t i l i z a t i o n was considered a c o l l o i d a l aggregation p r o c e s s . " 3.2.5 BIOCHEMISTRY AND COLLOIDS. But the most f r u i t f u l f i e l d of colloidology was one whose absence in a l l the tributes we have gone through above is remarkable. In 'The Physical Basis of L i f e ' Hardy states common wisdom about the role of proteins: The central chemical problem of l i v i n g matter [is] the chemical structure of proteid [Hardy, 1906, p. 446]. In Bechhold's Colloids in Biology and Medicine we can read also, in 1919: [The l i v i n g c e l l i s ] a c i t y in which c o l l o i d s are the houses and the c r y s t a l l o i d s are the people who traverse the streets, disappearing into and emerging from the houses, or who are engaged in demolishing or erecting buildings. The c o l l o i d s are the stable parts of the One phenomenon allegedly explained within colloidology was anaphylaxis, "anaphilactoid phenomena" (Bayliss, 1923] or, in general, phenomena related with what i s named today "antigen-antibody" reaction. A careful analysis of the debates in favor and against c o l l o i d a l interpretation of those can be found in [Mazumdar, 1974]. 131 organism, the c r y s t a l l o i d the mobile part, which penetrating everywhere may bring weal or woe (as quoted in (Tauber, 1937]). If the c o l l o i d s are the houses and buildings, what i s their p a r t i c i p a t i o n in the dynamics of chemical change? How are we to interpret the absence of ferments (or enzymes) in these formulations, after a l l those pronouncements about the c e n t r a l i t y of the 'enzyme theory' we saw in the l a s t chapter? By today's meanings there is no puzzle, as enzymes are presently recognized as protein molecules, but at the root of the quandary about the chemical nature of enzymes between 1900-1930 was the issue of how chemical processes go on in the c e l l . To see t h i s i t is necessary to look in some d e t a i l at the development of biochemistry. Frederick Gowland Hopkins' school represents more than any other the s p i r i t of the emerging d i s c i p l i n e of biochemistry during the f i r s t 40 years of t h i s century. Hopkins' pres i d e n t i a l address to the Physiological Section of the B r i t i s h Association for the Advancement of Science in 1913, e n t i t l e d 'The Dynamical Side of Biochemistry' [Hopkins, 1913] i s considered nowadays the exposition of the fundamental tenets of intermediary metabolism "It i s remarkable how the development of biochemical knowledge followed the course he had foreshadowed", his colleage Marjorie Stephenson observed [Stephenson, 1949]. To him, the th e o r e t i c a l obstacle to the advancement of knowledge on the chemical workings of the c e l l was the 'biogen' concept, a view which, as we saw 132 above, Hopkins and Fletcher had rejected in their discussion of muscle physiology. In more general terms Hopkins stated here his rejectio n of 'biogen* as an "obsession" such that the r e a l l y s i g n i f i c a n t happenings in the animal body are concerned in the main with substances of such high molecular weight and consequent vagueness of molecular structure as to make their reaction impossible to study...[Hopkins, 1913]. Why 'high molecular weights' necessarily implies consequence 'vagueness of molecular structure' i s so obvious for Hopkins that he does not find i t necessary to explain further. Statements l i k e t h i s , present a l l along in his papers, are motivated by his unequivocal d i s t r u s t of 'biogen', and are taken also to show Hopkins' rejec t i o n of proteins as macromolecules . s c > Hopkins emphasized his own approach: My main thesis w i l l be that in the study of the intermediate processes of metabolism we have to deal not with complex substances, which elude ordinary chemical methods, but with simple substances undergoing comprehensive reactions [Hopkins, 19131. & ° Hopkins apparently did not parti c i p a t e in the sometimes b i t t e r debate on the nature of proteins and enzymatic mechanisms, either the aggregate theory (the properly c o l l o i d a l theory) or the macromolecule one, although evidently he d i s l i k e d the concept of 'huge molecules'. P i r i e has an anecdote about i t : The large size of molecules r e s u l t i n g from Svedberg's centrifuge "caused Hopkins considerable d i s t r e s s , for he feared the reappearance of the vague concepts he abhorred. I well remember his consternation when I pointed out... that there was not enough matter in the universe... to make simultaneously one molecule of each of the isomers of a protein with 200 amino acids in i t " [ P i r i e , 1962]. 133 The research of Hopkins and his colleages went almost unaffected by t h i s misconception because the 'small molecules' he is r e f e r r i n g to are substrates. In this address he describes in a general way the experimental methods of intermediary metabolism: st r u c t u r a l considerations allow hypotheses about what the intermediary products are. Then, an animal i s fed or inoculated one of these. If i t is completely metabolized, then, very l i k e l y i t i s an intermediate step. Or, taking advantage of the "eclecticism of the body" (his words), they give the b i o l o g i c a l specimen molecules not exactly the same as the normal ones, and draw conclusions from the chemical r e s u l t s . Their technical problem was not, then, the chemical handling of huge molecules, but the separation and detection of small molecules that as intermediates do not accumulate, but exist in low concentrations. But how do the reactions occur? For the dynamic chemical events which happen within the c e l l , these c o l l o i d complexes y i e l d a special milieu ... but in the c e l l i t s e l f , I believe, simple molecules undergo reactions of the kind we have been considering. These reactions, being catalyzed by c o l l o i d a l enzymes, do not occur in a s t r i c t l y homogeneous medium...[Hopkins, 1913] . Then he continues with one of his more widely repeated statements on the c e l l : 134 The l i f e [of the c e l l ] is the expression of a pa r t i c u l a r dynamic equilibrium which obtains in a polyphasic system [Hopkins, 1913, p. 220]. As for his r e j e c t i o n of associating the l i f e of the c e l l with one particular big molecule c a l l e d biogen, the statement is clear. But i t i s not clear at a l l about the nature of enzymes and enzymatic action. "[E]ach chemical reaction within the c e l l is directed and controlled by a s p e c i f i c c a t a l y s t " (Ibid, p. 221), and these enzymes are of a c o l l o i d a l nature -- which means, given his r e j e c t i o n of big molecules, that they are aggregates. F i n a l l y , the c o l l o i d s of the c e l l offer a special milieu for chemical changes to occur, chemical changes that very l i k e l y are catalyzed by surfaces, and the whole c e l l i s a polyphasic system. What enzymes are, then, and how they act, i s l e f t rather obscure. Presiding at one of the sessions in the meeting about "Colloid Science Applied to Biology", Hopkins repeated his views: With the b i r t h of modern physical chemistry there arose, I think, in many minds the b e l i e f that i t was destined to provide in i t s e l f an adequate approach and a short cut to a re a l understanding of the nature of l i v i n g systems. Its data are, indeed, essential to any such understanding. But those dynamic events and the diverse chemical reactions which, within the l i v i n g c e l l , provide energy and s p e c i f i c chemical synthesis, are as much part of the essence of l i f e as the behavior of the c o l l o i d a l apparatus in which they occur. Without them no c o l l o i d a l system whatever can display, save in some accidental and unreal aspects (of which the importance is often exaggerated), the attributes of l i f e . We have come to believe that the l i v i n g c e l l , considered from 135 i t s most general aspects, is a system in which surface c a t a l y s i s controls many and diverse chemical events, while the high degree of coordination and organization to which these events a t t a i n may be due in some way to the nature and architecture of the c o l l o i d a l apparatus in which they progress... [Hopkins, 1930, p. 770]. 3.2.6 ENZYMES AS COLLOIDAL CATALYSTS When the measurement of reaction rates involving enzymes started i t was soon realized that the law of mass action did not hold. The rate of sugar inverted by acid is proportional to the concentration of sugar at any moment: -dC/dt = kC as in the reaction CizH^asOi i + H-20 y 2C©Hxa.Os while the concentration of water remains to a very good approximation constant. This is what is expected from the law of mass action for t h i s reaction. Then, the rate of reaction diminishes with time. But in the presence of invertase, k is not a constant, but increases with time and more generally in most enzymatic reactions i t diminishes. On the other hand, i t was found that when enzymes are present in low concentrations, during the i n i t i a l stages the reaction rate remains constant. 136 These r e s u l t s , which are just some examples of the f a i l u r e of the mass-action law does to hold, were explained from the very beginning with the hypothesis of the formation of enzyme-product compounds as intermediates to the formation of products. The v e l o c i t y of the formation of products would depend then on the concentration of these compounds, and a big the o r e t i c a l issue was the nature of these intermediary compounds. As part of the series 'Monographs on Biochemistry' whose editors were R.H.A. Plimmer and Hopkins himself, William M. Bayliss published in 1908 the book The Nature of Enzyme Action, a book that by 1925 was in i t s f i f t h e d i t i o n . Although there was not a uniform position on the mechanism of enzyme action, Bayliss' was one of the more popular ones in the 1910's. At the beginning of his book Bayliss singles out the main theme of the relations between c o l l o i d s and enzymes: It would be u n f r u i t f u l , in the present state of knowledge, to discuss in further d e t a i l the various hypotheses put forward to explain c a t a l y s i s . One of these, however, i s of importance in connection with c o l l o i d a l c a t a l y s i s , such as enzymes are, namely, surface-condensation of the reacting bodies, in which case the accelerated rate of change i s , in a l l pr o b a b i l i t y , due to increase of concentration [Bayliss, 1908, p. 51. As c o l l o i d s , enzymes w i l l be p a r t i c u l a r l y prone to form what we have c a l l e d 'adsorption compounds... [ C l o l l o i d s take up by adsorption various other bodies, and e s p e c i a l l y c o l l o i d s . . . These 'adsorption compounds', or c o l l o i d a l complexes as they are ca l l e d 137 by some when constituents are c o l l o i d s , play a very important part in enzyme action... ( i b i d , p. 16). Being c o l l o i d s , enzymes are capable of surface action; adsorption on t h e i r surfaces w i l l increase concentration, and in consequence the increased concentration would play an important role in rate enhancement. Bayliss makes clear what i s for him the nature of the intermediate substrate-enzyme compound: i t is an "adsorption compound". Enzyme action w i l l be in good part a surface e f f e c t . This fact w i l l have important consequences for the stoichiometry of the f i r s t step of the reactions catalyzed by enzymes: It is very important to bear in mind that a l l these c o l l o i d a l reactions have both a physical and chemical aspect. Certain c o l l o i d s , have a special adsorptive a f f i n i t y for one another, which is not purely chemical, since i t follows the law of adsorption and not those of constant combining proportion. This fact i s of great importance with regard to enzymes... It must be c l e a r l y understood that i t i s only the preliminary combination of enzyme and substrate that follows the law of adsorption. After close association has taken place, the proper chemical actions, due to the agency of the enzyme, begin to make their appearance [Bayliss, 1908]. P a r t i c u l a r l y r e f e r r i n g to his experimental model, the hydrolysis of proteins by trypsin, Bayliss found that the formation of the enzyme-substrate compound as a c o l l o i d a l complex would r e a d i l y explain the k i n e t i c a l behavior: the s p e c i f i c a c t i v i t y , that i s , 138 the r a t i o between mean v e l o c i t y and concentration, is greater for lower concentrations of tr y p s i n . If we make the reasonable assumption that the rate of change i s in proportion to the amount of "compound" of enzyme and substrate in existence at the time, i t w i l l be seen that the re s u l t i s what would be expected i f th i s combination were of the nature of an adsorption compound, since more trypsin w i l l be in association with the substrate in proportion to the concentration of the enzyme when the l a t t e r i s lower [Bayliss, 1908]. One of the arguments he uses to support his theory of the nature of the enzyme-substrate compound i s i t s resemblance with inorganic c o l l o i d c a t a l y s t s : That t h i s state of a f f a i r s is due to the c o l l o i d a l nature of enzymes, and therefore an adsorption phenomenon, i s indicated by the f a c t . . . that in the c a t a l y s i s of hydrogen peroxide by c o l l o i d a l metals the same kind of law holds, contrary to what obtains in the inversion of cane sugar by hydrion, where the law of proportionality holds [Bayliss, 1908, p. 60]. Bayliss is well aware that he has to account for the high s p e c i f i c i t y involved in enzyme action, as suggested by Emil Fischer with the key-lock simile in 1898 when he summarized his long work on enzyme action on sugars. The chemical nature of the surface or i t s molecular geometry can, wrote Bayliss, p e r f e c t l y explain i t . The effect of el e c t r o l y t e s and neutral s a l t s on enzymatic reactions seemed suitable to be approached with the same kind of 139 arguments used to explain other features of the general behavior of c o l l o i d s : the formation of the enzyme-substrate compound required a favorable r e l a t i o n of e l e c t r o s t a t i c charges, and the adsorption of free e l e c t r o l y t e s in solution on the surface of the enzyme (and of the substrate, i f i t is a c o l l o i d i t s e l f , as in the case of p r o t e o l y t i c enzymes) could a l t e r that r e l a t i o n . S l Bayliss's stance changed very l i t t l e in his 1923 book. As for the mechanism of rate enhancement he added the fact that adsorbed p a r t i c l e s on the surface of a c o l l o i d aggregate are s p a t i a l l y oriented, which may render these p a r t i c l e s more suitable for a s p e c i f i c a l chemical reaction. On the other hand, he i n s i s t s on the central theme of colloid-chemistry, surface action: It is now generally recognized that the enzymes which play so important a part in the speeding up of chemical reactions in l i v i n g organisms are a p a r t i c u l a r class of heterogeneous c a t a l y s t s . In other words, they are c o l l o i d s , and the reactions which they accelerate occur in the surface of the dispersed phase... In the f i r s t place, [there i s ! the e f f e c t of degree of dispersion on the a c t i v i t y of the enzyme. The greater the number of p a r t i c l e s into which a given mass of agent i s subdivided, the greater is the surface of a c t i v i t y [Bayliss, 1923]. S 1 Other views on the nature of the enzyme-substrate compound were suggested, and Bayliss himself c i t e s V. Henri's assumption in 1903 of a stoichiometric one-to-one compound. L. Michaelis's work during the 1910's, using the hypothesis of a stoichiometric compound and monitoring pH c a r e f u l l y in getting the data became important only by the end of the 1920's, after Sumner and Northrop succeeded in c r y s t a l l i z i n g complex proteins and afer the publication of J. B. S. Haldane's book The Enzymes. 140 3.2.7 THE FADING OF BIOCOLLOIDOLOGY In the minds of the students of the phenomena of l i f e during t h i s period, the chemical machine was unravelling i t s secrets: i t was a c o l l o i d a l machine. Colloids provided the buildings of the factories inside the c e l l , buildings conceived as an apparati able to provide a high degree of coordination and organization, while the chemical processes themselves were effected by the surfaces of c o l l o i d a l c a t a l y s t s , perhaps the walls of the same buildings. This looks l i k e a polyphasic system complex enough to allow a high number of correlated events in an o v e r a l l pursuit towards equilibrium. The celebrated b i o l o g i c a l order was at hand! But i t did not work out. During the 20's the magic of c o l l o i d s began to disappear. More than 20 years after his 'The physical basis of l i f e ' , Hardy himself observed: The mystery of l i f e is as great as i t was [40 years ago]... Nothing i s to be gained claiming l i v i n g matter as c o l l o i d a l . . At present the c o l l o i d a l kingdom seems to be an A l s a t i a wherein d i f f i c u l t states of matter find refuge from a too exacting enquiry [Hardy, 1928, p. 744]. By then A.V. H i l l had shown that the muscle could not be a surface machine by c a l c u l a t i n g that there could not be enough surface area for the required energy; the adsorption-compound as a f i r s t step in the process of enzymatic action was extensively 141 rejected but, most espec i a l l y , no clear breakthrough was obtained with the use of the tools offered by c o l l o i d o l o g i s t s . Meanwhile, another pattern of explanation was emerging with new tools, new concepts, and new sources of models to imagine the unknown: the explanation through macromolecules. s z The t h e o r e t i c a l change that overthrew colloidology can be looked from two points of view. The f i r s t addresses the change brought about by the set of new experimental results and new physico-chemical interpretations that shook the support of the t y p i c a l c o l l o i d a l explanation. C o l l o i d a l chemistry, as we saw, appealed to the idea of "aggregates* when re f e r r i n g to ' c o l l o i d a l p a r t i c l e s ' , l i k e proteins, and considered many physiological events such as enzyme action to be surface phenomena. With respect to t h i s , I w i l l discuss b r i e f l y the work of Jacques Loeb on the chemical behavior of proteins, Richard W i l l s t a t t e r on the p u r i f i c a t i o n of enzymes, James B. Sumner and J.H. Northrop on Of, course, there were s t i l l strong advocates of the c o l l o i d a l approach, among them, Ross Aiken Gortner in the United States. His Outlines of Biochemistry, [Gortner, 1929], was an extensive t r e a t i s e on c o l l o i d s . Almost 300 pages out of 750 are 'pure colloidology', and in the scarce 30 pages devoted to enzymes, statements l i k e the following can be read: "According to the older viewpoint the catalyst was looked upon as a mysterious chemical compound which in some way speeded up a reaction. According to the newer viewpoint a catalyst is looked upon as a source of surface energy, the chemical nature of the catalyst being r e l a t i v e l y unimportant providing that the space configuration of the atoms in the surface of the catalyst are such as to cause certain oriented adsorption relationships and the surface of the catalyst i s in such a state as to contribute a given quantity of surface energy to the system [Gortner, 1929, p. 708] . 142 c r y s t a l l i z a t i o n of enzymes and Theodor Svedberg with the ultracentrifuge. The second point of view deals with the new sources of models for the machine view of l i v i n g organisms which I w i l l discuss in the next section. In 1922 Jacques Loeb, at that time working in The Rockefeller Institute for Medical Research in New York, published the book Proteins and the Theory of C o l l o i d a l Behavior. Here he contended that the aggregate view of proteins - and in consequence i t s associated explanations - i s wrong. If enough care i s devoted to measure and maintain pH values during the experiments, he argued, proteins w i l l behave in solution just as individual chemical e n t i t i e s . E l e c t r o l y t e s are not 'adsorbed' at the surface of proteins, but they form valence bonds in a stoichiometric way. That i s , these products are not c o l l o i d a l complexes. They are molecules. When the hydrogen ion concentrations are duly measured and considered, i t is found that proteins combine with acids and a l k a l i e s according to the stoichiometrical laws of c l a s s i c a l chemistry and that the chemistry of proteins does not d i f f e r from the chemistry of c r y s t a l l o i d [Loeb, 19241. A protein molecule would remain in solution i f the forces between i t and the molecules of solvent are strong enough. Otherwise, the protein molecules coalesce, forming small s o l i d aggregates which w i l l remain in suspension i f e l e c t r o s t a t i c charges allow the formation of Helmholtz's double e l e c t r i c a l layer. 143 Experimental results of undeniable relevance against the aggregation view of proteins were obtained by Theodor Svedberg (1884-1971) using his ultra c e n t r i f u g a t i o n technique. Svedberg developed the technique and the associated t h e o r e t i c a l tools as part of his long study of the fundamental properties of c o l l o i d a l systems, e s p e c i a l l y the use of d i f f e r e n t i a l sedimentation to assess the size of aggregates. After some improvements of his f i r s t ultracentrifuge he decided to measure the degree of dispersion of some proteins, hemoglobin being his f i r s t success. But, contrary to his own expectations, he reported in 1926 that the solution of hemoglobin was monodisperse and that the l a t t e r ' s molecular weight was quite large: approximately 68000 D. His most surprising r e s u l t was finding that some proteins (hemocyanins) could have sharply defined molecular weights of the order of millions of daltons. Loeb's and Svedberg's researches were about the nature of proteins, but the idea that enzymes are proteins was only entertained for a short time at the beginning of the century and was abandoned when attempts at p u r i f i c a t i o n and i s o l a t i o n proved to be extremely d i f f i c u l t . As pointed out at the beginning of this section, 'enzyme' was a term defined operationally by the chemical effects brought about by preparations of usually unknown chemical composition. 'Something' was supposed to be 'in there', and this 'something' was responsible for catalyzing chemical 144 changes. Finding what that 'something* is proved a d i f f i c u l t endeavour. By 1909 the English physiologist W. Halliburton in the Annual Report of the Progress of Chemistry f e l t the necessity of warning about the increasing use of the •ferment-in-there' idea: We must take care in the twentieth century that the adoption of a new phrase, "ferment action", is not considered in i t s e l f to be a f i n a l solution of v i t a l problems. To label any pa r t i c u l a r change as due to enzyme a c t i v i t y should be rather a signal for the commencement of renewed research in attempts to understand i t s t i l l further (as quoted in [Kohler, 1964 ] ) . Bayliss himself, acknowledging that no great progress had been made after Buchner's report of the zymase extract to i d e n t i f y i t s exact chemical nature, gave some support to an hypothesis formulated even before Buchner's announcement: When we consider the way in which d e f i n i t e chemical properties diminish more and more as the preparations are p u r i f i e d , we see a certain degree of j u s t i f i c a t i o n for the view expressed by De Jagger and Arthus [in 1890 and 1896, r e s p e c t i v e l y ] , that enzymes are not chemical individuals, but that various kinds of bodies may have conferred upon them properties which cause them to behave l i k e enzymes; so we have to deal with properties rather than substances [Bayliss, 1908, p. 20]. A view l i k e t h i s was a c t i v e l y sponsored in 1922 by A. Fodor, who supported the view that "enzymes are not to be regarded as special chemical individuals of peculiar chemical structure, but as known constituents of protoplasm, merely having a special degree of c o l l o i d a l d i s p e r s i t y " [Waldschmidt-Leitz, 1929]. As 145 late as 1932, at the meeting 'On Recent Advances in the Study of Enzymes and th e i r Action', Richard W i l l s t a t t e r was s t i l l far from considering that the quandary was solved: Enzymes in most cases are only characterized, at the s t a r t and for a long period [by their a c t i v i t y ] , ... as long as nothing can be said concerning their chemical composition. It is to be remembered that the constitution of an enzyme cannot be determined in the same way as the structure of simpler substances such as hormones and vitamins... [ W i l l s t a t t e r , 1932] The school more thoroughly committed to the search for the chemical nature of enzymes during the 1910's and 20's was that of W i l l s t a t t e r and his associates (mainly Ernst Waldschmidt-Leitz) in Munich and l a t e r in Zurich. Their main endeavour was the p u r i f i c a t i o n of enzymes as the only evident way to assess their s p e c i f i c i t y and chemical nature. To accomplish t h i s , W i l l s t a t t e r devised the method of looking for s p e c i f i c adsorbants to which an enzyme preparation was exposed; afterwards, the system was washed with mild chemical methods to free the adsorbed substance from the adsorbant and the procedure repeated again and again. A summary of W i l l s t a t t e r ' s school's findings can be read in Enzyme Action and Properties by E. Waldschmidt L e i t z , published in 1929. Claims that enzymatic reactions do not comply with the law of mass action are found but with no experimental evidence; the interaction i s stoichiometrical instead of adsorption-like, but a small dependence on the degree of dispersion induced 146 W i l l s t a t t e r to adopt a sort of intermediate position between the purely chemical and the purely c o l l o i d a l approach: W i l l s t a t t e r considers ... that the enzymes are composed of a c o l l o i d a l bearer and a s p e c i f i c , active group, which enables them to be bound to the substrate, and the composition of which at the same time conditions the c o l l o i d a l nature of the entire complex. Such a concept gives equal value to the physico-chemical and to the s t r u c t u r a l chemical behavior of the enzymes. [Waldschmisdt-Leitz, 1929]. In 1926 J.B. Sumner working in the US reported he had c r y s t a l l i z e d the enzyme urease taken from jack beans. Sumner's preparation was highly active, which meant a high degree of purity, and gave positive results to tests for protein. W i l l s t a t t e r did not agree that this was a proof that enzymes are proteins. Other enzymes, he claimed, did not give such positive r e s u l t s . In addition, what Sumner had obtained is an active preparation of the enzyme that includes i t s protein c a r r i e r . Sounding a l i t t l e s a r c a s t i c , W i l l s t a t t e r pointed out at the meeting of the Royal Society on enzyme action quoted above: While the Munich laboratory endeavoured to pu r i f y enzymes so that they should be more and more free from protein, Sumner and Northrop, by contrast, have employed the methods for the c r y s t a l l i z a t i o n of proteins to produce enzymatically active preparations in the form of proteins [ W i l l s t a t t e r , 1932]. But other enzymes were soon c r y s t a l l i z e d , and i t was shown that some tests used to detect the presence of proteins in some 147 preparations were not sensi t i v e enough, which explained other negative results [Tauber, 1937]. By the middle of the 1930's a l l enzymes were known to be proteins, a l l of them also molecules of rather high molecular weight. The l a s t , and weak, stronghold of the c o l l o i d movement seemed to be surrendering. 3.3 THE AGE OF COLLOIDOLOGY Between the years 1900 and 1920 the term c o l l o i d and i t s associated concepts were invoked i f not to explain at least to point the way to an explanation for events occurring in the c e l l , be they p a r t i c u l a r , such as c e l l c o n t r a c t i l i t y , or of a general kind, such as enzymatic c a t a l y s i s . The pervasive presence of the c o l l o i d o l o g i s t 1 s baggage allows us to dub the period 'the age of c o l l o i d o l o g y ' . S 3 Part of the prestige of c o l l o i d a l science in physiology could have been borrowed i n c i d e n t a l l y from unrelated achievements in other realms. The so-called f i r s t experimental evidence of the existence of atoms came from Perrin's measurements of and the application of Einstein's theory to Brownian motion, a c o l l o i d phenomenon. Millikan's experiment was performed also in a c o l l o i d system, a dispersion of l i q u i d drops in gas. C o l l o i d o l o g i s t s seemed to be aware of thi s transferred prestige. When an itin e r a n t cycle of lectures was organized in the United States during 1925 and 1926, Robert M i l l i k a n was in charge of the f i r s t t a l k , 'Principles underlying c o l l o i d chemistry', which, despite the t i t l e , he devoted e n t i r e l y to the existence of the electron and to his method of a l t e r i n g the charge of the c o l l o i d a l o i l droplets. 148 One can f i n i s h reading a modern biochemistry textbook without seeing the word " c o l l o i d " even once. The book Proteins, Amino  Acids and Peptides as Ions and Dipolar Ions, a landmark in the physico-chemical study of proteins, written by Edwin J. Cohn and John T. Eds a l l and published in 1943 [Cohn, 1943], does not have the word c o l l o i d in i t s a n a l y t i c a l index (and very l i k e l y not anywhere in i t s more than 400 pages). s* In 1948 J.D. Bernal decided that his turn had come to write his own essay on The  Physical Basis of L i f e [Bernal, 1951]. There he recalled the term c o l l o i d in the following way: Un t i l the advent of the electron microscope, a great blank existed between the knowledge of atomic combinations provided by chemistry and that of h i s t o l o g i c a l structures observable with the microscope. This gap was f i l l e d with the mystic word " c o l l o i d " , which served to explain the very real but very obscure properties depending on the existence of structures of magnitudes between ten and ten thousand Angstroms. Now the c o l l o i d world i s open for inspection, and the term i t s e l f w i l l probably vanish or acquire precise and limited meaning [Bernal, 1951]. Marcel F l o r k i n , co-editor for many years of the huge c o l l e c t i o n Comprehensive Biochemistry and himself a h i s t o r i a n of biochemistry, labeled the period "the dark age of biocolloidology" [Florkin, 1972], The crystallographer John C. Kendrew blamed the c o l l o i d o l o g i s t s for lack of f a i t h : s * The book i s dedicated, among others, to Hardy and Loeb, as pioneers in the physico-chemical study of l i v i n g matter. 149 The concept of structure i t s e l f became ascribed to b i o l o g i c a l molecules only at a f a i r l y recent date. The r e a l l y important b i o l o g i c a l molecules, such as the nucleic acids and the proteins, are d i f f i c u l t to handle by c l a s s i c a l chemical methods; and their old c l a s s i f i c a t i o n , as c o l l o i d s , was a confession of ignorance and at the same time of lack of f a i t h [Kendrew, 1969]. With similar arguments Kendrew could blame for lack of f a i t h those researchers s t i l l finding m i c e l l e - l i k e structures in solutions of soap in water. Colloidology was in i t s e l f a sound f i e l d of research, as can be inferred from the account given in th i s chapter, and sound also were the claims about the appropriateness of i t s tools to deal with phenomena inside the c e l l . Its use as a speculative tool to explore behavior not completely understood is not at a l l d i f f e r e n t from the contemporary speculative appeal to huge molecules suggested in order to explain not completely clear physiological events by means of th e i r imagined capacity simply to be able to do i t . To this speculative role of concepts I want to refer now. Biocolloidology was not just a set of concepts to deal with physical and chemical changes in protein solutions of r e l a t i v e l y simple composition caused by the addition of some e l e c t r o l y t e s . C o l l o i d a l behavior represented also a pa r t i c u l a r conception of what a chemical machine may be l i k e so i t can account for l i f e processes as well as being consistent with current theore t i c a l t o o l s . To detect what characterizes c o l l o i d a l models as d i f f e r e n t 150 from those molecular models that were going to replace them, an argument commonly used by Bayliss may be re c a l l e d here: It might, perhaps, be supposed that i f the process of subdivision were carried farther and farther u n t i l molecular dimensions were reached, the phenomena due to surface would be more and more manifest. In point of fact, however, th i s is not the case; although we know nothing of what the molecular state e s s e n t i a l l y i s , we do know that bodies in t h i s condition do not show the properties of matter in mass, i . e . , bounded by surfaces [Bayliss, 1908, pp. 13-14] The physical d i s c o n t i n u i t y that Bayliss points out here implies a choice in the th e o r e t i c a l tools you count on to tackle a problem. For a given question w i l l you have to be a physicist or a chemist? There is implied also a preference in the kind of mechanisms that are going to be proclaimed as those producing the multifarious events of the c e l l as a 'chemical machine'. In the section on muscle models in the l a s t chapter I referred to the general differences between the surface models -- which in fact, were c o l l o i d a l — and the presently accepted ones, re l y i n g on s o l i d - l i k e molecules. The former ones are 'molar' mechanisms, for which descriptions in terms of bulk properties are used. When surface effects are considered as the main issue in c a t a l y t i c a c t i v i t y , and the account of rate enhancement is regarded lar g e l y to be a consequence of increased concentration at surfaces, molar mechanisms are being invoked. But when enzyme action is changed from a surface phenomenon to a molecular interaction the mechanism of enzyme action w i l l be looked as a mechanical 151 'alternative' way for two molecules to react. If enzymes are considered as c o l l o i d a l aggregates and enzyme action as some kind of surface action, molar mechanisms are associated with enzymatic c a t a l y s i s . They were replaced by another way of thinking about physiological matters: molecular mechanisms. As the aggregate view of the "world of neglected dimensions" was replaced with the macromolecular view, the physiological models of the c e l l ' s marvels were replaced by the alleged behavior of macromolecules. Since the working of a machine requires s o l i d - l i k e features, i t was inevitable that the new kinds of models were preceded by the general acceptance of the existence of huge molecules in the c e l l , as was described in the end of the l a s t section. In fact, the ups and downs of the modern be l i e f in big b i o l o g i c a l molecules coincides remarkably well with the ups and downs of the place of the macromolecule concept in organic chemistry. Zandvort [Zandvort, 1988] divides the l a t t e r in three periods. From 1860 to 1900 a s t r u c t u r a l i s t , chemical view was held by the majority of chemists, following ideas mainly originating in Kekule's model of valence which recognized no l i m i t to the size of a molecule. Then, between 1900 and 1925 a physical view, that of aggregates, was dominant and i t was common for chemists to say that the investigation of these substances should be l e f t to p h y s i c i s t s . F i n a l l y , from 1925 on, e s p e c i a l l y after 1935, the chemical view, whose great advocate was the German chemist Hermann Staudinger, d e f i n i t e l y overthrew the aggregation view. 152 Staudinger's macromolecule was not, however, the same big molecule as that of the biochemist. According to what they then ca l l e d the chemical view, natural and a r t i f i c i a l polymers behave in solution as independent molecules, separated by molecules of the solvent. But the polymers have neither a precise molecular weight nor a defined structure. What the c r y s t a l l i z a t i o n of proteins showed, and later x-ray d i f f r a c t i o n results confirmed, is the aperiodic c r y s t a l nature of most b i o l o g i c a l macromolecules. The h i s t o r i a n of science Robert C. Olby has suggested the inclusion of the notion of macromolecule in the history of molecular biology [Olby, 1979]. We have seen that the adversaries of the 'biogen', 'inogen' and similar concepts during the f i r s t decades of t h i s century generally did not address the question of the existence of big molecules. To them, a big molecule was synonymous with lack of structure. On the other hand, when Zandvort traced the history of the notion of macromolecule, the only reference he made to studies in b i o l o g i c a l f i e l d s i s to Olby's a r t i c l e . The idea that big molecules do not exi s t , or are so i n d i s t i n c t as not to deserve the name molecule, apparently was so widespread that i t was not even worth mentioning. The obvious relevance of well defined macromolecules to sustain a properly-c a l l e d machine of molecular dimensions strongly backs Olby's contention. I would dare to suggest that the existence of the aperiodic s o l i d is the main breakthrough leading to molecular biology in i t s broad sense. Curiously enough, t h i s was the view adopted by Schrodinger in his immensely popular (and misread) book What i s L i f e ? . As we saw in the second chapter, the mechanists of the XVIIth century, p a r t i c u l a r l y Boyle, appealed to molecular operations similar to those operations occurring in the macroscopic world. The suggestion rendered poor r e s u l t s , as can be seen from the fact that chemistry developed following quite d i f f e r e n t l i n e s . But although chemistry and physics f i n a l l y arrived at a point where they can say that Newton's program of action at a distance is the triumphant one, biochemical models of physiological workings look in some way similar to what Boyle envisioned. We are returning to Boyle's models, but this time Newton would not say that hooked atoms do not explain anything. Hooks indeed can be found with x-rays or electron microscopy techniques, 'Van der Waals r a d i i ' replaced contact repulsive forces and a f f i n i t i e s replaced molecular wedges. The dynamics of the system is now the integrated operation of myriads of minuscule machines. The analogy between the dynamics of the macroscopic world and the c e l l i s established through the operation of molecular machines. 154 A . MOLECULAR MACHINERY 'Molecular machinery' has become a catchy phrase. Nowadays saying that the c e l l is a chemical machine f a l l s too short as a reca p i t u l a t i o n of the most fashionable view of the workings of the unit of l i f e . As usually happens with these brief metaphorical expressions, i t s power as a speculative instrument resides in i t s two-fold feature of leaving a good range of unprecisely s p e c i f i e d analogies and disanalogies to work on and at the same time summarizing in an image many debates and results in the history of ideas about the subject in which i t is embedded and about i t s relations with related d i s c i p l i n e s and associated worldviews. To begin to see what is implied by the metaphor of a molecular machine, some examples are worth exploring. A s t r i k i n g one is the f a t t y acid synthetase complex which synthesizes palmitic acid (a saturated f a t t y acid having 16 carbons) in higher animals. 155 After 'activating* the f i r s t two contributing molecules -- acetyl CoA and malonyl CoA, i t s e l f a modification of acetyl CoA — the synthetase complex proceeds with an enzymatic reaction (a condensation step) at the end of which four of the future 16 carbons form a small chain at the t a i l end of a moeity attached to a protein that makes up part of the complex. Three successive enzymatic reactions w i l l arrange carbons and hydrogen into the form CH3 CH^ C • • • A new step of condensation comes next, another molecule of malonyl CoA serving as the donor of two more carbon atoms, and the condensation step is followed again by the same reactions that occurred in the f i r s t cycle. At the end of th i s second cycle six of the future 16 carbon atoms are in place with their respective hydrogens. The cycle repeats again and again u n t i l the hydrocarbon chain i s completed, and f i n a l l y another enzymatic reaction releases the f a t t y acid from the complex. Six enzymes act orderly in seven cycles to produce one molecule of palmitic acid. In higher animals the six enzymes are assembled in t h i s synthetase complex. In the middle of the complex i s placed another protein provided with a 'movable arm'. Thermal fluctuations move t h i s arm which holds the growing f a t t y acid 156 molecule so i t can go orderly from the active s i t e of one enzyme to the active s i t e of the next, to have the respective work done on i t (see figure 3, taken from [Fox, 1982]). By a sort of metaphor whose l i t e r a l realm is the macroscopic contrivance t h i s supermolecule i s assimilated to a machine: movement of s o l i d - l i k e parts are arranged in a s p e c i f i c way to produce a coherent and c y c l i c behavior. s e 5 e = The chemical reactions are very nearly the same in E.  c o l i , but here the enzymes are not arranged in this sort of complex and in consequence the process i s not as e f f i c i e n t as in higher animals. However, we can say that these kinds of coordinated reactions are conceived from the beginning with machine-like features in mind. NADPH F i g . 3. The f a t t y acid synthetase complex, after having finished the f i r s t cycle (taken from [Fox, 1982] ) . 157 The o v e r a l l reaction i s described as follows: Acetyl CoA + 7 malonyl CoA + 14 NADPH + 7H+ > > palmitate + 7C0 2 + 14 NADP+ + 8CoA + 6H20 but considering the reactions rendering malonyl CoA from acetyl CoA, C0 2 and ATP, i t can be rewritten: 8 Acetyl CoA + 7 ATP +14 NADPH > > palmitate + 14 NADP+ + 8CoA + 6H=0 + 7ADP f 7P± Written in thi s way with the p a r t i c i p a t i o n of ATP, i t can e a s i l y be calculated that the reaction has a t o t a l negative change in free energy, and w i l l be said to be 'thermodynamically p o s s i b l e 1 . The previous description of the complex renders a sketch of how the reaction takes place, but, apart from other features, i t leaves aside one c r u c i a l point: how is energy harnessed to overcome the energetically unfavorable steps? The evident f i r s t way of building a tolerable explanation of how processes in an organism can go ' u p h i l l ' was the one used, for example, in Liebig's late model of the muscle. After an input-output evaluation i t is said that the energy provided by the foodstuffs w i l l account for the energy necessary for muscle 158 contraction. As for 'coupling', phenomena similar to those occurring in heat machines were r e c a l l e d : in the case of Liebig's Spannkraft, a big specialized molecule is presumed to receive energy from i t s surroundings, accumulating i t in the form of c o n t r a c t i l e or expansive power. Later the mechanical energy so stored i s released and macroscopic work i s performed. To understand the central issues of processes l i k e this i t is necessary to look in some d e t a i l into the operation of a heat machine. Heat can come either from the surroundings or, as in an internal combustion engine, i t may appear as the r e s u l t of the fuel's transformation into more stable substances. In the l a t t e r s i t u a t i o n , energy stored in the configurational degrees of freedom of molecules is transferred to thermal degrees of freedom. The heat machine, an appropriate arrangement of s o l i d s (considering the times and temperatures involved), is designed in a way that allows i t to take small b i t s of energy from the thermal degrees of freedom and to store them in a change of configuration of a 'mechanical reservoir', for example, by l i f t i n g a weight in a g r a v i t a t i o n a l f i e l d , or compressing a spring. To produce the mechanical e f f e c t , then, in an internal combustion machine chemical energy i s converted into heat energy, and the subsequent drop in the l a t t e r accounts d i r e c t l y for the appearance of energy accumulated in mechanical degrees of freedom (in t h i s instance, of course, macroscopic degrees of freedom). 159 The argument shows what is brought from heat machines when models l i k e Liebig's Spannkraft for conversion of chemical energy into energy stored in macroscopic mechanical degrees of freedom are suggested. During the years of biocolloidology 'thermodynamical models' were also suggested for processes of chemical synthesis in the organism. It was known that in humans ingested proteins are degraded completely into amino acids before any process of synthesis b e g i n s . e e Protein synthesis was an almost intractable problem, but there was the suggestion that since enzyme catalyzed reactions are r e v e r s i b l e , a high concentration of amino acids could drive the reaction toward synthesis. It was proven so in  v i t r o . but i t was recognized at the same time that high concentrations of amino acids are not detected in the tissues. Ross Aiken Gortner struggled, nevertheless, to keep a l i v e the p l a u s i b i l i t y of the thermodynamical model of protein synthesis: It seems highly probable that the synthesis within the tissues may be brought about by a similar mechanism [to in v i t r o synthesis with p r o t e o l y t i c enzymes] and that an e f f e c t i v e high concentration of amino acids may res u l t from the 'binding' of a large part of the water within the c e l l , thus e f f e c t i v e l y concentrating the amino acid to a point where synthesis in the presence of p r o t e o l y t i c enzymes takes place [Gortner, 1929, p. 433 ]. There is one contrivance whose arrangement supposedly permits a chemical reaction to go ' u p h i l l ' using d i r e c t l y the chemical s s A "discovery of a p e c u l i a r i t y in metabolism which to the biochemist represents a very fortunate aspect of a f f a i r s " , said Hopkins in a memorable address in 1916 [Hopkins, 1916]. 160 energy stored in other part of the system. Two electrochemical c e l l s can be arranged in series in such a way that the e l e c t r i c a l current generated in one of them is used to produce a chemical reaction in the other. S 7" Two metal electrodes (for s i m p l i c i t y we can consider the same metal) are immersed in two separate and di f f e r e n t concentrations of a s a l t of the metal. The two solutions are connected, as usual, through a s a l t bridge. The di f f e r e n t concentrations w i l l generate a potential difference between the electrodes, and equilibrium is reached between each electrode and i t s solution when the exchange of ions between them is balanced. A chemical process starts after connecting the two electrodes through an external c i r c u i t containing another chemical c e l l , for example, an el e c t r o l y z e r , in which water is separated into hydrogen and oxygen. The flow of electrons into one of the electrodes lowers the potential barrier obstructing the metal ions* adsorption on the electrode, and now slower ions would be able to reach the metal. Something similar occurs on the other metal electrode. Heat rushes into the solutions from the thermal reservoir (the atmosphere in t h i s case), keeping the temperature constant. It i s t h i s energy that is being used to produce the e l e c t r o l y s i s ! In spite of the apparent differences & 7 This s i t u a t i o n was discussed by C.W.F. McClare [McClare, 1971 and 1974] and later in more d e t a i l by L. Blumenfeld. McClare (who died in 1977) was probably the f i r s t one to begin a thorough discussion about the implication of treating molecules as machines. Here I am following Blumenfeld's argumentation [Blumenfeld, 1983 and 1981], but he himself follows McClare's conclusions. 161 from a heat machine, in th i s s i t u a t i o n again chemical changes in the electrolyzer are produced by thermal energy. Before giving more detailed examples to grasp the differences between macroscopic machines and molecular machines found or suggested in l i v i n g tissues, i t is convenient to adopt the terminology commonly used in the l i t e r a t u r e . In a one-phase system a thermodynamic potential, the Gibbs free energy, has the property that in a process where p and T are held constant (as in most chemical reactions in so l u t i o n ) , dG = -dW0 where dW0 indicates work d i f f e r e n t from pV, that i s , d i f f e r e n t from work of expansion. It i s important to remark that thermodynamics is not a theory that can provide expressions for dW0 by deduction from i t s p r i n c i p l e s . These arise either from the o r e t i c a l considerations — conceivable systems or models -- or must be induced from the experimental r e s u l t s . Thus, we know that springs (or rubber) would be able to perform work due to e l a s t i c i t y , and the expression for i n f i n i t e s i m a l work in the case of a spring ('an e l a s t i c system') w i l l be fdL. The creation of a surface is a process needing expenditure of energy, or t h e o r e t i c a l l y we can suppose that molecules on the surface are in d i f f e r e n t conditions than molecules in bulk, define a c o e f f i c i e n t 162 to account for the difference, and then match experimental results with the new term gdS. In a physicochemical system having only one phase and one chemical species, then, we have \ G = G(p, T, X i , X 2, ...) where the variables X t, X 2 are extensive variables appropriate for the system according to observation, and then dG = -dXx (^G/oXi) - ... where (^G/^XJ... are intensive variables related to the respective work-yielding event. Each expression for i n f i n i t e s i m a l work, then, can be written as the product of change of an intensive factor (i>G/^X x . . . ) and a d i f f e r e n t i a l expressing an i n f i n i t e s i m a l change of configuration: dW„ = - fdL - gdS - vdQ where dL i s a change in the length of a linear e l a s t i c system, dS a change of surface area, dQ a change in the amount of charge accumulated in a place were the e l e c t r i c potential i s v. If the system comprises d i f f e r e n t chemical species and d i f f e r e n t phases, the Gibbs free energy w i l l be a function of 163 G = G(p, T, X w X 3 / N i , N 2, ...) with N i , N 2, ... denoting the number of moles of d i f f e r e n t chemical species in spec i f i e d phases, the change of free energy during a process with T and p constant w i l l be expressed as: dG = -dXi ()>G/lXi) - ...-jJLidnx - |U,2dn2 - ... where each Jn,i — the so c a l l e d chemical potential — is equal to ^G/^n ±. These additional d i f f e r e n t i a l s are expressions of what is cal l e d chemical work, and they describe changes due to chemical reactions or movement of chemical species from one phase to another. For chemical processes going on in solution, l i k e those in a l i v i n g organism, description of changes in terms of changes in free energy instead of changes in internal energy is usually adopted. If after some process the energy accumulated in one of the possible ways to describe the configuration increases while another one decreases i t is said that a free energy transduction has occurred. If the exchange in forms of energy storage is caused by the operation of a par t i c u l a r piece of the c e l l ' s machinery, the l a t t e r i s described as a 'free energy transductor'. 164 The drawing in figure 4 (taken from [Peusner, 1974]) i l l u s t r a t e s the idea of free energy transduction. Driving reaction Driven reaction B F i g . 4. Metaphorical picture of a transduction process (from [Peusner, 1974]). A process thermodynamically able to occur by i t s e l f drives another process that alone cannot happen. The drawing depicts a transductor, in thi s case a gearing, which is a t y p i c a l s o l i d device characterized by input work = output work Do devices l i k e these occur in l i v i n g organisms? Can they be molecules? What kind of processes are used to drive and what kind of processes are driven? These are the sorts of questions we must answer when the existence of molecular machines is postulated. Suppose there i s a membrane separating two compartments. In the l e f t compartment two neutral non-reacting molecular species are in a higher concentration than in the right compartment. The d i f f u s i o n of any or both species w i l l lower the free energy of the system, and they w i l l migrate i f the membrane separating both phases is permeable to them. Now, given some concentration, the free energy change due to the d i f f u s i o n of one of the species could be used, in p r i n c i p l e , to carry molecules of the other species against i t s concentration gradient, i f the combined processes give a t o t a l negative free energy change. Again, i t i s important to look a l i t t l e closer at thi s process. The macroscopic r e s u l t , changes in concentration in both phases, is due to a net resu l t of molecules spontaneously migrating from each side to the other. Two molecules of the same species that are close to the membrane but in d i f f e r e n t compartments w i l l have the same proba b i l i t y , independent of concentration, of crossing the membrane to the other compartment. 166 This kind of transduction process is quite common in c e l l s . For example, non equilibrium concentrations of Na* are thought to drive glucose across the plasma membrane against the l a t t e r ' s concentration gradient. But although the process is thermodynamically feasible by i t s e l f , i t involves the p a r t i c i p a t i o n of separate molecular devices -- free-energy molecular transducers — c a l l e d 'glucose pumps' [Alberts et. a l . , 1988, pg 310]. The phrase 'separate molecular devices' here implies that the macroscopic process r e s u l t i n g in a measurable flux of chemical species is the sum of individual exchange processes accomplished by molecular devices. 'Molecular devices' here means more than just 'mechanisms of molecular dimensions'; i t means that the devices are molecules, in the same sense that enzymes are molecules. In her account of the debate about anaphylactic reaction Pauline Mazumdar [Mazumdar, 1974] says about Loeb's 1922 book -- in which Loeb argued that proteins are molecules — that Loeb managed to destroy with [his arguments] not only the application of c o l l o i d a l analogies to the antigen-antibody reaction, but the entire assumption that proteins needed a special set of laws to account for their reaction... Curiously, Loeb had produced in 1921 a very passionate declaration in favor of a mechanistic conception of l i f e with examples drawn from plant tropisms and from parthenogenesis in eggs induced by inorganic means, but none of his examples, then, were as good an argument against v i t a l i s m as t h i s one turned out to be [my emphasis]. 167 Loeb's position turned out to be that in the physiological realm, •hammers are molecules'. 'Physiological hammers* — an expression I use to denote those devices responsible for most microphysiological process — turned out to react with acids and bases just as any other simple substance. They are just molecules, an amazing r e s u l t , in fact, as can be made clear rephrasing i t with the aid of an example: the 1two-potassium-three-sodium-ions-ATP-splitter-translocator' turns out to be a substance, that i s , i t comes in molecules. e e Why Mazumdar denounced as v i t a l i s t s those researchers thinking otherwise — for instance, that surfaces are responsible for these processes -- i s not clear at a l l . If we compare the heat machine and the electrolyzer in series with a galvanic c e l l , on the one hand, with the coupling of flows existing in b i o l o g i c a l membranes on the other, we find that in both the o v e r a l l macroscopic event is the outcome of elementary acts which are ' b i t s ' of the process. The upward movement of a piston is caused by elementary acts of c o l l i s i o n between a microscopic body and a macroscopic one, each elementary c o l l i s i o n y i e l d i n g a 'bit of expansion'. The coupled flow of chemical species in the example of the membrane i s also the outcome of elementary acts, small ' b i t s ' of translocation. But in the l a t t e r s i t u a t i o n , the macroscopic phenomenon i s seen to involve the The example refers to the sodium-potassium ATP-ase pump, which is discussed below. 168 p a r t i c i p a t i o n of 'third e n t i t i e s ' that after the elementary act return to the i r i n i t i a l conditions to accomplish a new elementary act. Each microscopic ' b i t ' is the resu l t of a complete cycle of operation of one of these 'third e n t i t i e s ' . This feature i s even displayed by those simple enzymatic reactions where the catalyzer enhances the v e l o c i t y of a chemical process with t o t a l negative free energy change, no coupling being necessary. The reaction is accomplished with the p a r t i c i p a t i o n of a molecular machine providing the elementary acts of chemical transformation, a machine that operates repeatedly going through almost the same set of configurations. The molecular devices responsible for the free-energy transduction between Na* and glucose gradients are not the most interesting ones from the point of view of what a molecular device i s thought to be able to perform. If, a transduction process l i k e t h i s exchange of small molecules is to occur continuously, the non-equilibrium concentrations of the 'driving' chemical species must be restored. To do t h i s , a number of separate molecules c a l l e d Na"*"-K"* pumps move Na* out of the c e l l against i t s electrochemical potential gradient and at the same time move K* into the c e l l , also against i t s electrochemical potential g r a d i e n t . S 9 A 'coupling' must exist with other process S 9 This i s quite far from being an irrelevant example. Today i t is considered that one th i r d of the ATP consumed by a resting animal i s spent in t h i s pumping that maintains the c e l l out of equilibrium [Stryer, 1988, p. 950]. When a muscle is contracting i t becomes indeed a large consumer of metabolic 169 that guarantee a t o t a l negative free-energy change. Here another sort of free energy transduction is displayed: part of the Na""-K* pump i s a Na*-K* ATP-ase. One molecule of ATP i s s p l i t into ADP and P*, and the excess free energy of thi s reaction is used to translocate three sodium ions and two potassium ions against their thermodynamic tendency. Chemical energy stored in the internal conformational degrees of freedom of one molecule, ATP -- mostly, though not only, in the bond between the l a s t phosphate and the rest of the molecule — is used in each act of translocation. However, this i s anything but a small heat machine.7'0 Part of the chemical energy of the one-molecule system ATP is stored by the molecular machine — I repeat: a substance! — the 1Na*-K* pump' which uses i t then for the translocation process. A transduction process similar to t h i s , in the sense that chemical energy taken from one molecule is "stored" in a larger one so that the l a t t e r can do work, takes energy, but the fact that for many decades muscles were conceived as the user of metabolic energy par excellence shows that the animal machine was considered as existing mostly at equilibrium. 7 - 0 The most popular model for the process of oxidative phosphorylation -- the chemiosmotic theory -- shows, interes-t i n g l y , central features of a heat machine. Small 'b i t s ' of energy given by H* ions moving 'downhill' are r e l a t i v e l y slowly accumulated u n t i l enough energy is available to establish the high energy bond of ATP. 170 place in each elementary act of muscle contraction, as was described in the previous chapter. However small, the t i n y devices are allegedly able to perform coherent changes of configuration, a c h a r a c t e r i s t i c which immediately brings to mind that they necessarily have a s o l i d -l i k e structure. In phase space, the machine -- a protein --undergoing conformational t r a n s i t i o n s traverses a f a i r l y constant path again and again. This is e n t i r e l y conceivable in macroscopic devices where fluctuations a f f e c t the operation in a minimal way, but i t is surprising in molecular devices, even in b i o l o g i c a l macromolecules, e s p e c i a l l y in coupling, when the machine i s thought to 'store' energy and to deliver i t , thus doing work. The protein-machines have movements resembling the macroscopic motion of everyday machines. And when they store energy in s p e c i f i c degrees of freedom they must be able to prevent them from exchanging with thermal degrees of freedom. McClare c a l l s such processes "mechanical" : "A mechanical process is either one in which heat is not exchanged, so that the only 7 , 1 "Stored" i s the word commonly used, but I put i t in quotation marks because i t can be another extension of the machine metaphor. It is loosely used to designate something that must happen -- some chemical facts and the conservation of energy force the conclusion that energy must come from, stay or go somewhere but how i t happens i s less known. In the animal body energy can be "stored" in ATP as gas i s stored in an automobile. But, how is the energy o r i g i n a l l y contained in individual molecules used to drive a change that otherwise would mean the increase in t o t a l free energy? flow of energy is between forms that remain stored" [McClare, 1971]. These mechanical ones are clockwork-like mechanisms, and in part that is why I stated at the end of the last chapter that Boyle's idea has been revived. The age of biocolloidology, with i t s models obtained from a physical chemistry dominated by thermodynamics, represents the h i s t o r i c a l pinnacle of the idea that small macroscopic systems describable by thermodynamics could be able to explain microphysiological events. The ups and downs of the molecular devices -- the machine metaphor taken to the molecular realm — that became the favorite speculative instrument of biochemistry and molecular biology have not been thoroughly analyzed. Definite landmarks are Lipmann's suggestion that ATP is the 'combustible* for chemical changes going u p h i l l , the discovery of the structure of DNA with the mechanism for b i o l o g i c a l r e p l i c a t i o n springing naturally from i t , as the separation of the strands and the synthesis of a complementary thread in each strand. F i n a l l y , I w i l l mention the Singer and Nicholson f l u i d mosaic model. Certain microphysiological events, for which a protein layer on the  surface of the c e l l was considered responsible, according to the model of Dawson and D a n i e l l i , were after the acceptance of the 172 Singer and Nicholson model considered to be caused by individual protein molecules now f l o a t i n g i n the membrane of the c e l l l i k e icebergs in the ocean. These model making a c t i v i t i e s are a l l connected. The success of the DNA molecular machinery encouraged the idea that other molecular machines e x i s t . The success of the hypothesis that proteins are molecules -- and the other hypothesis that enzymes are proteins — gave b i r t h to an appreciation that most microphysiological processes are due to the existence of molecular machines operating in l i v i n g things. 173 5. EPILOGUE History of ideas seems nowadays a discredited approach for writing history of science. Dr. X. made t h i s experiment or observation, obtained these r e s u l t s , induced this theory, published these books and a r t i c l e s , rejected or accepted those results and theories on such and such grounds, and so on. If the account is directed to j u s t i f y the most recent fashionable theory, i t is c a l l e d Whiggish history. If i t is too f a i t h f u l to the multitude of hypotheses and researchers i t becomes a meaningless account. The history of 'molecular biology', in the broad sense, as a history of ideas has preferred to whirl around theoret i c a l and experimental breakthroughs: the consolidation of the idea that DNA is the molecular species responsible for hereditary characters, the unraveling of i t s structure, the discovery of RNA. In the approach I have pursued in t h i s essay I have t r i e d to follow h i s t o r i c a l l y the way in which the machine metaphor, 174 sometimes hidden, sometimes openly debated, was present as a constraint and as a guide -- as i f the models themselves were trying to find a c t u a l i z a t i o n as viable machines -- in exploring hypotheses about the workings of the b i o l o g i c a l i n d i v i d u a l . Kant suggested that nature is necessarily categorized by man under his a p r i o r i concepts of space and time. Canguilhem insinuated that "a certain technological and pragmatic structure of human perception in the matter of organic objects showed up the condition of man [as] an organism [and] maker of machines" [Canguilhem, 1961]. Today more than ever man regulates his l i f e in order to feed and to take care of the machines he has b u i l t as extensions of his body and c a p a b i l i t i e s . And now, more than ever, he is eager to understand himself as a being similar to what he has been able to bu i l d . 175 BIBLIOGRAPHY Alberts, Bruce et a l . 1989. Molecular Biology of the C e l l . 2nd ed. New York & London: Garlan Publishing, Inc. Bayliss, William M. 1908. The Nature of Enzyme Action. London: Longmans, Green and Co. Bayliss, William M. 1923. The C o l l o i d a l State in i t s Medical  and Physiological Aspects. London: Henry Frowde and Hodder & Stoughton. Bayliss, William M. 1924. P r i n c i p l e s of General Physiology. 4th ed. New York: Longmans, Green and Co. Bernal, John D. 1951. The Physical Basis of L i f e . London: Routledge and Keagan. Black, Max. 1962. Models and Metaphors. Ithaca (NY): Cornell University Press. Blumenfeld, Leon .A. 1981. Problems of B i o l o g i c a l Physics. Springer-Verlag Series in Synergetics 7. B e r l i n : Springer. Blumenfeld, Leon A. 1983. Physics of Bioenergetic Processes. Springer-Verlag Series in Synergetics 16. B e r l i n : Springer. Boyle, Robert. 1772. The Works of the Honourable Robert Boyle. Ed. Thomas Birch. 6 Vols. Germany: Scientia Verlag Aalen, 1965. Brown, Theodore M. 1974. "From Mechanism to Vitalism in XVIIIth Century English Physiology." J. Hist. B i o l . 7, No. 2 ( F a l l ) . Campbell, N. R. 1920. Foundations of Science. New York: Dover Publications. 176 Canguilhem, George. 1952. "Machine et organisme." La  connaissance de l a v i e . Paris: Vrin, 1965. Canguilhem, George. 1961. "The Role of Analogies and Models in B i o l o g i c a l Discovery." S c i e n t i f i c Change. Ed. A.C. Crombie. London: Heineman. Cantor, Geoffrey N. 1982. "Weighing Light: The Role of Metaphor in XVI11-Century Optical Discourse." The Figural and the  L i t e r a l ; Problems of Language in the History of Science and  Philosophy. Eds* A.E. Benjamin, G.N. Cantor and R.R. C h r i s t i e . Manchester (Eng): Manchester University Press. Carnap, Rudolph. 1966. Philosophical Foundations of Physics. New York: Basic Books, Inc. Coley, Noel G. 1973. From Animal Chemistry to Biochemistry. Amersham: Hulton Educational Publications. Cohn, Edwin J., et a l . 1943. Proteins r Amino Acids and  Peptides as Ions and Dipolar Ions. New York: Reinhold. Cranefield, Paul. 1957. "The Organic Physics of 1847 and the Biophysics of Today." J. Hist. Med. 12. Descartes, R. 1972. Treatise of Man. Cambridge (Mass): Harvard University Press. Dijksterhuis, E.J. 1961. The Mechanization of the World  Picture. Oxford: Clarendon Press. Dixon, Malcolm. 1970. "The History of Enzymes and B i o l o g i c a l Oxidations." The Chemistry of L i f e . Eight Lectures on the  History of Biochemistry. Ed. Joseph Needham. Cambridge (Eng): Cambridge University Press. Donnan, F.G. 1929. "The Phenomena of L i f e . " Scientia 45. Eco, Umberto. 1983. The Name of the Rose. San Diego: Harcour, Brace, Jovanovich. Elkana, Yehuda. 1974. The Discovery of the Conservation of  Energy. London: Hutchinson Educational. Engelmann, T.H. 1895. "On the Nature of Muscular Contraction." Proc. Roy. Soc. (London). P. 411. Fletcher, W.M. and F.G. Hopkins. 1917. "The Respiratory Process in Muscle and the Nature of Muscular Action." Proc. Roy. Soc. B  (London) 89. 177 F l o r k i n , Marcel. 1972. A History of Biochemistry. Comprehensive Biochemistry 30. Amsterdam: El s e v i e r . Fox, Ronald F. 1982. B i o l o g i c a l Energy Transduction: The  Uroboros. New York: John Wiley and Sons. Frank, Robert G, J r . 1980. Harvey and the Oxford Physiologists. Berkeley: University of C a l i f o r n i a Press. Freyhofer, Horst H. 1982. The Vitalism of Hans Driesch. European University Studies. Frankfurt/M.-Bern: Peter Lang. Fruton, Joseph S. 1972. Molecules and L i f e . New York: Wiley. Gol i n s k i , Jan V. 1982. "Robert Boyle: Skepticism and Authority in XVIIth Century Chemical Discourse." The Figural and the  L i t e r a l ; Problems of Language in the History of Science and  Philosophy. Eds A.E. Benjamin, G.N. Cantor and R.R. C h r i s t i e . Manchester (Eng): Manchester University Press. Goodfield, G.J. 1960. The Growth of S c i e n t i f i c Physiology. London: Hutchinson. Gortner, Ross A. 1929. Outlines of Biochemistry. New York: John Wiley & Sons, Inc. Gottfried, Kurt and Victor F. Weisskopf. 1984. Concepts of  P a r t i c l e Physics. New York: Oxford University Press. Graham, Thomas. 1861. "Liquid Diffusion Applied to Analysis." In: Chemical and Physical Researches. Edinburgh: T. & A. Constable, 1876. H a l l , Thomas S. 1970. "Descartes Physiological Method: Position, P r i n c i p l e s , Examples." J. Hist. B i o l . 3 No. 1 (Spring) Haraway, Donna. 1976. C r y s t a l , Fabrics and F i e l d s : Metaphors of  Organicism in XXth Century Developmental Biology. New Haven (Conn): Yale University Press. Harden, Arthur. 1911. Alcoholic Fermentation. London: Longmans, Green and Co. Hardy, William B. 1899 "On the Structure of the C e l l Protoplasm." Collected S c i e n t i f i c Papers of Sir William Bate  Hardy. London: Cambridge University Press, 1936. Hardy, William B. 1906. "The Physical Basis of L i f e . " Collected S c i e n t i f i c Papers of Sir William Bate Hardy. London: Cambridge University Press, 1936. 178 Hardy, William B. 1928. "Living Matter." Collected S c i e n t i f i c  Papers of Sir William Bate Hardy. London: Cambridge University Press, 1936. Hein, Hilde S. 1971. On the Nature and Origin of L i f e . New York: McGraw H i l l . Hesse, Mary. 1966. Models and Analogies in Science. Notre Dame (Indiana): University of Notre Dame Press. Hobbes, Thomas. 1968. Leviathan. Baltimore: Penguin Books. Hobbes, Thomas. 1966. "Elements of Philosophy. The F i r s t Section Concerning the Body". The English Works of Thomas Hobbes. Ed. Sir William Molesworth. Second reprint, Vol. I Germany: Scientia Verlag Aalen. Holmes, Frederic L. 1975. "The Transformation of the Science of Nutr i t i o n . " J. Hist. B i o l . 8, No. 1 (Spring). Holmes, Frederic L. 1963. "Elementary Analysis and the Origins of Physiological Chemistry." ISIS 54, Part I, No. 175. Hopkins, Frederic G. 1930. "Introductory Remarks." C o l l o i d Science Applied to Biology, Part II: The Structure of Living Matter. Trans. Farad. Soc. 26. Hopkins, F.G. 1916. "Newer Standpoints in the Study of Nutr i t i o n . " Hopkins and Biochemistry. Ed J. Needham. Cambridge (Eng): W. Heffer, 1949. Hopkins, F.G. 1913. "The Dynamical Side of Biochemistry." Nature 92, p. 220. Huxley, Andrew. 1980. Reflections on Muscle. Liverpool: University Press. Jaynes, J u l i a n . 1976. The Origin of Consciousness in the  Breakdown of the Bicameral Mind. Boston: Houghton M i f f l i n Company. Kendrew, John C. 1969. "Physics, Molecular Structure, and Bio l o g i c a l Function." Biology and the Physical Sciences. Ed. Samuel Devons. New York: Columbia University Press. Klemm, F r i e d r i c h . 1964. A History of Western Technology. Cambridge (Mass): The MIT Press. Kohler, Robert E. 1964. "The Enzyme Theory and the Origins of Biochemistry." Is is 63. 179 Kuhn, Thomas S. 1979. "Metaphor in Science." Metaphor and  Thought. Ed. Andrew Ortony. Cambridge University Press. Kuhn, Thomas S. 1977. "Second Thoughts on Paradigms". The  Structure of S c i e n t i f i c Theories. Ed. F. Suppes. Urbana (111.): University of I l l i n o i s Press. Kuhn, Thomas S. 1969. "Reflections on my C r y t i c s . " C r i t i c i s m  and the Growth of Knowledge. Ed. Imre Lakatos. Cambridge (Eng): Cambridge University Press. La Mettrie, J u l i e n Offray de. 1987. Man a Machine. La Salle (111) : Open Court. Laszlo, Pierre. 1986. Molecular Correlates of B i o l o g i c a l  Concepts. Comprehensive Biochemistry 34a. Amsterdam: E l s e v e i r . Lenoir, Timothy. 1982. The Strategy of L i f e : Teleology and  Mechanics in 19th Century German Biology. Holland: Dodrecht. Liebig, Justus. 1843. Animal Chemistry, or Organic Chemistry in  i t s Application to Physiology and Pathology. London: Taylor & Walton. Loeb, Jacques. 1924 Proteins and the Theory of C o l l o i d a l  Behavior. 2nd ed. New York: McGraw-Hill Book Co. Macallum, A.B. 1913. "The Origin of Muscular Energy: Thermodynamic or Chemodynamic?" J. B i o l . Chem. 14. Mazumdar, Pauline. 1974. "The Antigen-Antibody Reaction and the Physics and Chemistry of L i f e . " B u l l . Hist. Med. 48. McClare, C.W.F. 1974 "Resonance in Bioenergetics." The  Mechanism of Energy Transduction in Bi o l o g i c a l Systems. Annals of the New York Academy of Sciences 227. McClare, C.W.F. 1971. "Chemical Machines, Maxwell's Demon and Living Organisms." J. Theor. B i o l . 30. McCormack, Earl R. 1985. A Cognitive Theory of Metaphor. Cambridge (Mass): The MIT Press. Nagel, Ernst. 1961. The Structure of Science. New York: Harcourt, Brace & World, Inc. Needham, Dorothy. 1972 Machina Carnis: The Biochemistry of  Muscular Contraction in i t s H i s t o r i c a l Development. London: Cambridge University Press: London. Newton, I. 1952. Opticks. New York: Dover Publications. 180 Oesper, R.E. 1945. J. Chem. Ed. 22, p. 263. Olby, Robert C. 1979. "The Significance of the Macromolecules in the Historiography of Molecular Biology." Hist. P h i l . L i f e .  Sciences 1, No. 2. Ostwald, Wolfgang. 1919. A Handbook of Co l l o i d Chemistry. London: J & C h u r c h i l l . Partington, J.R. 1964. A History of Chemistry. Vol. 4. London: MacMillan & Co, Ltd. Pepper, Stephen. 1961. World Hypotheses: A Study of Evidence. Berkeley (Ca): University of C a l i f o r n i a Press. Peusner, Leonardo. 1974. Concepts in Bioenergetics. Englewood C l i f f s (NJ): Prentice H a l l , Inc. P i r i e , N.W. 1962. "Patterns of Assumptions about Large Molecules." Archives of Biochemistry and Biophysics. Supp. 1, pp 21 - 29. Roe, Shirley A. 1984. "Anatomia Animata: The Newtonian Physiology of Albrecht von Haller." Transformation and Tradition  in the Sciences. Ed. Everett Mendelsohn. Cambridge (Eng): Cambridge University Press. Roe, Sh i r l e y A. 1981. Matter L i f e and Generation. Cambridge (Eng): Cambridge University Press. Singer, Charles. 1989. A History of Biology to about the Year  1900. Ames: Iowa State University Press. Sourkes, T. L. 1955. "Moritz Traube, 1826-1894: His Contributions to Biochemistry." J. Hist. Med. 10. Stephenson, M. 1949. "Sir Frederic G. Hopkins Teaching and S c i e n t i f i c Influence." Hopkins and Biochemistry. Ed. J. Needham. Cambridge (Eng): W. Heffer. Stryer, Lubert. 1988. Biochemistry. 3rd ed. New York: W.H. Freeman and Co. Suppe, Frederick. 1977. The Structure of S c i e n t i f i c Theories. 2nd ed. Urbana (111): University of I l l i n o i s Press. Szent-Giorgyi, Albert. 1969. " F i f t y Years of Poaching in Science." Biology and the Physical Sciences. Ed. Samuel Devons. New York: Columbia University Press. 181 Szent-Gyorgyi, Albert. 1972. "Electronic Mobility in B i o l o g i c a l Processes." Biology, History and Natural Philosophy. Eds. Allend D. Breck and Wolfgang Yourgrau. New York: Plenum Press. Tauber, Henry. 1937. Enzyme Chemistry. New York: John Wiley and Sons, Inc. Toulmin, Stephen. 1977. "The Structure of S c i e n t i f i c Theories." The Structure of S c i e n t i f i c Theories. 2nd ed. Ed. Frederick Suppe. Urbana (111): University of I l l i n o i s Press. Turbayne, C o l i n . 1970. The Myth of Metaphor. Rev. ed. Columbia (South Carolina): University of South Carolina Press. Van't Hoff, J.H. 1967. Imagination in Science. B e r l i n : Springer-Verlag. Verworn, Max. 1899. "General Physiology; an Outline of the Science of L i f e " (Excerpts). A Source Book in Animal Biology. Ed. Thomas S. H a l l . New York: Haffner Publishing Co., 1964. Waksman, Selman A. 1926. Enzymes. Properties, D i s t r i b u t i o n .  Methods and Applications. Baltimore: The Williams and Wilkins Company. Waldschmidt-Leitz, E. 1929. Enzyme Actions and Properties. New York: John Wiley and Sons. Westfall, Richard. 1971. The Construction of Modern Science. New York: Wiley. W i l l s t a t t e r , Richard. 1932. "Discussion on Recent Advances in the Study of Enzymes and their Action." Transc. Faraday. Soc. B  (London) 111. Wilson, Edmund B. 1923. "The Physical Basis of L i f e . " Science 57, No. 1470. Wilson, Edmund B. 1928. The C e l l in Development and Heredity. 3rd ed. New York: The Macmillan Company. Woodger, J.H. 1929. B i o l o g i c a l P r i n c i p l e s . London: Routledge & Keagan. Zandvort, H. 1988. "Macromolecules, Dogmatism and S c i e n t i f i c Change: The Prehistory of Polymer Chemistry as Testing Ground for the Philosophy of Science." Studies in History and Philosophy of  Science 19, No. 4. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0076839/manifest

Comment

Related Items