222 DIGESTION. 



Composition of Gastric Juice. 



Human Sheep's Dog's 



Gastric Juice. Gastric Juice. Gastric Juice. 



Water, .... 994.40 986.14 971.17 



Solid Constituents, . . 5.- r >9 13.85 2882 



Solids. 



f Ferment, Pepsin (with 



a trace of Ammonia), 3.19 4.20 17.50 



Hydrochloric Acid, . 0.20 1.55 2.70 



Chloride of Calcium, . 0.06 0.1 1 1.66 



Sodium, . 1.46 4.36 314 



" Potassium, 0.55 1.51 1.07 

 Phosphate of Lime, 



[ Magnesia, and Iron, 0.12 2.09 2.73 



Iii all the above analyses the amount of water given must 

 be reckoned as rather too much, inasmuch as a certain quan- 

 tity of saliva was mixed with the gastric fluid. The allow- 

 ance, however, to be made on this account is only very small. 



Considerable difference of opinion has existed concerning 

 the nature of the free acid contained in the gastric juice, 

 chiefly whether it is hydrochloric or lactic. The weight of 

 evidence, however, is in favor of free hydrochloric acid, being 

 that to which, in the human subject, the acidity of the gastric 

 fluid is mainly due ; although there is no doubt that others, 

 as lactic, acetic, butyric, are not unfrequently to be found 

 therein. 



The animal matter mentioned in the analysis of the gastric 

 fluid is named pepsin, from its power in the process of diges- 

 tion. It is an azotized substance, and is best procured by di- 

 gesting portions of the mucous membrane of the stomach in 

 cold water, after they have been macerated for some time in 

 water at a temperature between 80 and 100 F. The warm 

 water dissolves various substances as well as some of the pepsin, 

 but the cold water takes up little else than pepsin, which, on 

 evaporating the cold solution, is obtained in a grayish-brown 

 viscid fluid. The addition of alcohol throws down the pepsin 

 in grayish-white flocculi ; and one part of the principle thus 

 prepared, if dissolved in even 60,000 parts of water, will 

 digest meat and other alimentary substances. 



The digestive power of the gastric fluid is manifested in its 

 softening, reducing into pulp, and partially or completely dis- 

 solving various articles of food placed in it at a temperature 

 of from 90 to 100. This, its peculiar property, requires the 

 presence of both the pepsin and the acid ; neither of them can 

 digest alone, and when they are mixed, either the decomposi- 

 tion of the pepsin, or the neutralization of the acid, at once 



