C 45 ] 
III. On the nature of the acid and saline matters usually ex- 
isting in the stomachs of animals . By William Prout, 
M. D. F. R. S. 
Read December 11, 1823. 
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 Spallan- 
zani. This illustrious philosopher concluded, from his nume- 
rous experiments, that the gastric fluids, when in a perfectly 
natural state, are neither acid nor alkaline. Even Spallan- 
zani, 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 indivi- 
dual 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 se- 
creted by that organ itself. The only account of Scopoli’s experiments I have 
seen is in Johnson’s Animal Chemistry, i. 183. 
t 
