382 



Man. 



Dog. 



Sheep. 



The specific gravity is 0-001 to 0-010. 



The special characteristic of this juice is its acidity. This has four 

 main functions: 



1. To kill ingested bacteria in the stomach, and thus (a) inhibit the 

 entry of pathogenic organisms into the body, and (6) prevent the early 

 putrefaction of the ingested food. 



2. To facilitate protein digestion. 



3. To liberate the hormone secret in from its precursor in the duo- 

 denal mucous membrane, and thus excite the flow of juices from the 

 pancreas and liver. 



4. To induce a flow of intestinal juice in the duodenum. 



In regard to the first function, it has been shown that the acidity 

 of the juice in guinea-pigs is sufficient to kill the cholera vibrio or 

 bacillus. If, however, the gastric juice were first neutralized, the 

 introduction of the bacilli killed the animals. 



Apart from pathogenic bacteria, it is important that bacteria 

 which split proteins and carbohydrates be kept in check ; otherwise 

 a large part of the ingested food would be wasted. 



Meat mixed with gastric juice, or a dead frog in a snake's stomach, 

 will keep sweet and free from putrefaction for days. 



A considerable amount of controversy has taken place in regard 

 to the nature of this acidity. It was at first believed to be due to lactic 

 acid. That it is due to hydrochloric acid is shown conclusively by 

 the fact that in an analysis of the juice there are more chlorine atoms 

 found than can combine with all the bases. How far the acid is com- 

 bined or free in the secreted juice is a matter of doubt. Most of it is 

 probably not free in the chemical sense, but so loosely combined that 

 it is able to effect its physiological function. The difference is shown 

 thus: (1) A solution of pure hydrochloric acid of the same degree 

 of acidity, when heated quickly, gives off acid fumes; gastric juice 

 does not until a syrupy consistency of concentration is reached; 

 (2) hydrochloric acid of the same acidity will transform starch into 

 dextrins, gastric juice will not; (3) the inverting power of gastric juice 

 upon disaccharides is not so powerful as an equivalent strength of 

 hydrochloric acid. Nevertheless the acid in the pure juice certainly 

 reacts acid to such indicators as congo-red, dimethylaminoazobenzol, 

 and therefore may be termed " physiologically " active. HC1 is 

 freely dissociated into H and Cl ions in such dilutions as are found in 

 the stomach. Weak organic acids, such as lactic and butyric, are 



