200 HUMAN PHYSIOLOGY 



by the gastric juice. The enzyme is generally known 

 as pepsin. An acid medium is essential to its action. 



Solid proteins, like boiled white of egg, first swell in 

 gastric juice and then dissolve. If the sample is origi- 

 nally liquid, like raw white of egg, the change is just as 

 definite though it cannot be followed by the eye. Vari- 

 ous stages in the digestion have been described by in- 

 vestigators but they need not concern us. The products 

 which we may expect to find in the place of the original 

 protein after the usual period in the stomach are highly 

 soluble,- fairly diffusible, and bitter. They are spoken 

 of as peptones. They are susceptible of further cleavage 

 but this is more likely to be accomplished in the in- 

 testine than in the stomach. 



Fat Digestion in the Stomach. There is little change 

 in a pure fat, like butter or lard, during the time that it 

 remains in the stomach. Emulsified fats, like cream, 

 are acted upon to a limited extent, the products being 

 glycerin and fatty acids. The enzyme to which this 

 effect is credited is called gastric lipase. It is certainly 

 much less important than the lipase from the pancreas 

 which is to reach the food in the small intestine. What 

 we call the fat of meat is really something more than 

 fat in the strict sense. Fat is there in abundance but 

 it is retained by envelopes and fibers which are of a 

 protein character. The supporting material of the 

 adipose tissue is subject to peptic digestion and when this 

 is accomplished the true fat separates as an oil which the 

 gastric juice scarcely attacks. 



Fermentation in the Stomach. Emphasis has been 

 placed on the antiseptic virtue of the gastric juice. The 

 normal acidity prevailing after a meal is unfavorable 

 to most types of bacterial activity, but it is natural to 

 expect that if any kinds of organisms are permitted to 

 multiply they will be those which produce acid by their 

 own life-processes. There is usually some bacterial 

 decomposition going on in the stomach, affecting prin- 

 cipally the sugars, and yielding lactic acid as a chief 



