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Acidification of rectal fluid in the locust Schistocerca gregaria Speight, Janet Dorothy Isabella

Abstract

Acidification of rectal fluid in Schistocerca gregaria is due probably to active secretion of hydrogen ions, although bicarbonate absorption from H₂CO₃ leaving behind hydrogen ions cannot be excluded. This was concluded after the following mechanisms were eliminated: introduction of acid from some anterior region of the gut; bacterial fermentation; slow release of hydrogen ions from fecal material; preferential absorption of the basic form of the phosphate buffer pair; secretion of acid phosphate; release of hydrogen ions from the intima. Any absorption of phosphate in the rectum must be as the monovalent ion since the cuticular intima was found to limit severely passage of the divalent form, as shown by studies of intimal permeability at various pH values. The relationship of acidification of rectal contents to total acid-base regulation of the locust is not clear, although there is some evidence that excess acidity is lost via the excreta. Regulation of the hemolymph pH is rather slow, with a halfway return to normal in about one day when the tolerance level has not been exceeded.

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