III. On the nature of the acid and saline matters usually ex­isting in the stomachs of animals

Abstract

That a free, or at least an unsaturated acid usually exists in the stomachs of animals, and is in some manner connected with the important process of digestion, seems to have been the general opinion of physiologists till the time of Spallanzani. This illustrious philosopher concluded, from his nume­rous experiments, that the gastric fluids, when in a perfectly natural state, are neither acid nor alkaline. Even Spallanzani, however, admitted that the contents of the stomach are very generally acid ; and this accords not only with my own observation, but with that, I believe, of almost every indivi­dual who has made any experiments on the subject. With respect to the nature of this acid, very various opinions have been entertained. Some of the older chemists seem to have considered it as an acid, sui generis ; by others it was supposed to be the phosphoric, the acetic, the lactic acid, &c. No less various have been the opinions respecting After I had discovered the principal fact related in this paper, I was surprized to find how nearly Scopoli had come to the same conclusion. He did not indeed come to the conclusion, as far as I can ascertain, that free muriatic acid exists in the stomach, but he advanced the opinion, that the muriatic acid, in union with ammonia, found in such abundance in the stomach of ruminating animals, is secreted by that organ itself. The only account of Scopoli’s experiments I have seen is in Johnson’s Animal Chemistry, i. 183. its origin and use ; some supposing that it is derived from the stomach itself, and is essential to the digestive process; others, that it is derived from the food, or is a result of fementation, &c. ; in short, there seems to be no physiological subject so imperfectly understood, or concerning which there has been such a variety of opinions.