420 Dr. R. D. Tliomson o» the Digestion of 



ammoniac or a volatile muriate was present is proved by the 

 second result. 



It is well known that Dr. Prout by similar experiments 

 drew the conclusion that free hydrochloric acid was present in 

 the stomach. That distinguished chemist however omitted the 

 first experiment which I have described. Indeed he could not 

 have made it successfully under the circumstances in which he 

 operated, because the gastric juice in his experiments was not 

 exposed to a heat that could coagulate and separate the albu- 

 minous matters, which would then have combined with the 

 oxide of silver and have complicated the result. In the gas- 

 tric juice employed in the preceding researches, however, no- 

 thing was present but soluble starch or dextrin and sugar, 

 which formed obviously no compounds with silver, insolu- 

 ble in boiling nitric acid. It is possible, therefore, in the 

 experiments of Dr. Prout, who determined the total amount 

 of chlorine in the gastric fluid by supersaturating with pot- 

 ash, igniting and precipitating with nitrate of silver, that he 

 had formed cyanide of potassium, which would precipitate 

 cyanide of silver along with the chloride, unless the pre- 

 caution were taken not merely to add nitric acid, but to 

 boil the solution after the addition of the acid, since cyanide 

 of silver is insoluble, or at least not wholly decomposed by 

 cold nitric acid. I offer this explanation, originally proposed 

 by Leuret and Lassaigne, because from my knowledge of Dr. 

 Prout, I am quite certain his experiments were most accu- 

 rately made. Indeed, the testimony of all succeeding experi- 

 menters who have obtained the same results is sufficient to 

 establish his accuracy without the addition of any confirmation 

 on my part. It is even possible that, in cases where the food 

 is different, the acid maybeof the nature described by Dr. Prout. 



The experiments which have been detailed seem to demon- 

 strate that no free hydrochloric acid existed in the stomach of 

 the animal, under the circumstances described, since no acid 

 could be distilled over at a temperature greatly above that at 

 which this acid boils when sufficiently concentrated, while the 

 fluid in the retort became more intensely acid in proportion 

 as the distillation proceeded. A portion of the liquid from 

 the retort was evaporated to dryness and heated to a tempe- 

 rature exceeding 300° without giving out acid fumes ; the 

 residue was digested in water, and still retained an acid reac- 

 tion. The solution of this residue was easily saturated by 

 carbonate of lime, and was not precipitated by chloride of 

 calcium, indicating the absence of biphosphate of lime (contrary 

 to the views of Blondlot), and likewise of free sulphuric acid. 



In another experiment the gastric juice was evaporated to 



