GASTRIC JUICE, AND STOMACH DIGESTION. 139 



filtration from accidental impurities. Obtained in this way, the 

 gastric juice is a clear, watery fluid, without any appreciable vis- 

 cidity, very distinctly acid to test paper, of a faint amber color, 

 and with a specific gravity of 1010. It becomes opalescent on 

 boiling, owing to the coagulation of its organic ingredients. The 

 following is the composition of the gastric juice of the dog, based 

 on a comparison of various analyses by Lehmann, and Bidder and 

 Schmidt : 



COMPOSITION OF GASTRIC JUICE. 



Water 975.00 



Organic matter ......... 15.00 



Lactic acid 4.78 



/ 



Chloride of sodium ........ 1 70 



" " potassium 1.08 



" " calcium 0.20 



" ammonium ........ 0.65 



Phosphate of lime 1.48 



" " magnesia 0.06 



" " iron 0.05 



1000.00 



In place of lactic acid, Bidder and Schmidt found, in most of their 

 analyses, hydrochloric acid. Lehmann admits that a small quantity 

 of hydrochloric acid is sometimes present, but regards lactic acid 

 as much the most abundant and important of the two. Eobin and 

 Yerdeil also regard the acid reaction of the gastric juice as due to 

 lactic acid ; and, finally, Bernard has shown, 1 by a series of well 

 contrived experiments, that the free acid of the dog's gastric juice 

 is undoubtedly the lactic ; and that the hydrochloric acid obtained 

 by distillation is really produced by a decomposition of the chlo- 

 rides, which enter into the composition of the fresh juice. 



The free acid is an extremely important ingredient of the gastric 

 secretion, and is, in fact, essential to its physiological properties ; 

 for the gastric juice will not exert its solvent action upon the food, 

 after it has been neutralized by the addition of an alkali or an 

 alkaline carbonate. 



The most important ingredient of the gastric juice, beside the 

 free acid, is its organic matter or " ferment," which is sometimes 

 known under the name of pepsine. This name, "pepsine," was 

 originally given by Schwann to a substance which he obtained 

 from the mucous membrane of the pig's stomach, by macerating it 

 in distilled water until a putrid odor began to be developed. The 



1 Leqoiis de Physiologic Experimentale, Paris, 1856, p. 396. 



