THE PHYSIOLOGY OF DIGESTION i8i 



Young's experiments on frogs had already taught him, in confirma- 

 tion of Spallanzani, that the gastric juice resists decay and it " even 

 restored putrid substances to their original sweetness." Here is an 

 additional experiment upon himself: 



On an empty stomach I made a light dinner, on chicken pye, and drank 

 simple water: in half an hour, by irritating my fauces, it was thrown up; at 

 this time it was plentifully supplied with gastric fluid, as well as saliva, as the 

 quantity of food was but small. It was then exposed in a tumbler to a heat 

 equal to the human temperature. For the space of nine hours there was not 

 the least intestine motion nor any disengagement of air. As digestion is per- 

 formed sooner than this period, it was not attended to any longer. 



Young convinced himself of the acid character of the gastric fluid 

 and attempted to identify the acid present. 



A piece of fresh veal was introduced into the empty stomach of one of the 

 large frogs: in two hours it was examined; the surface was a little tender; 

 upon being touched with litmus paper it was turned red. Here digestion was 

 progressing quite regular, yet an acid was present. It appeared impossible at 

 the same time to conceive the meat could become sour in so very short a time, 

 and in so very low a temperature; it was therefore conjectured, the acid was to 

 be referred not to the meat, but to the gastric juice, which the following experi- 

 ments confirmed us in. A frog was kept starving for two days; a piece of 

 litmus paper was then forced into its empty stomach by means of a pair of 

 forceps; upon being drawn out, it was covered with gastric juice, and the litmus 

 turned red. The naked gastric juice was afterwards often examined, by bring- 

 ing it out of their stomachs with a teaspoon, and constantly found to be slightly 

 acid. Being thus fully persuaded the acid, in the digested food of frogs, did 

 not arise from a fermentation, but was to be referred to their gastric juice, we 

 were led by analogy to suppose the acid of our own stomachs was to be at- 

 tributed to the same origin: but this analogical reasoning might be called mere 

 probability; the following experiment was therefore performed. Early in the 

 morning, my stomach being empty, I irritated my fauces with a view of throw- 

 ing up some gastric juice: though many efforts were made, none could be 

 vomited. The following day I took some meat on an empty stomach: in half 

 an hour afterwards, by irritating my fauces, the meat was thrown up, and with 

 it some gastric fluid: upon being tested, an acid was very evidently present. 

 Here no one can suppose the acid was to be referred to the meat. We have 

 little hesitation, therefore, in saying that the acid so constantly found in the 

 stomach of man, and almost, probably, all animals, is to be referred to their 

 gastric fluid. 



Young's friend, ]\rr. Mitchell, " being in good health and having 

 the power to ruminate," collected gastric fluid for him. The analysis 

 of the filtered fluid was performed by precipitating with acetate of 

 lead. The precipitate was treated with muriatic acid " which decom- 

 posed it, a very white powder remaining at the bottom, and a fluid 

 above." From analogy with the behavior of urine similarly treated 

 the author concluded: 



Though great accuracy and many varied experiments are required to ascer- 

 tain certainly the presence of an unknown acid, yet we are disposed to believe 

 any person who had witnessed the great similarity in the comparative precipita- 



