198 GASTRIC DIGESTION 



like consistence. The result of the digestion of fibrin, in the gastric 

 juice or in an acidulated fluid to which pepsin has been added, is its 

 complete solution and transformation into a substance that is not 

 affected by heat, acids or by rennet. The substance resulting from the 

 action of gastric juice on fibrin, called fibrin-peptone, resembles the 

 albumin-peptones, but has certain distinctive characters. 



Liquid casein is immediately coagulated by the gastric juice, by 

 the action of both the free acid and an organic matter called rennin 

 (chymosin). Once coagulated, casein is acted on in the same way as 

 coagulated albumen. Casein taken as an ingredient of cheese is digested 

 in the same way. The casein of human milk, which coagulates only 

 into a sort of jelly, is more easily digested than casein from cow's milk. 

 The product of the digestion of casein is a soluble substance, not coagu- 

 lable by heat or the acids, called casein-peptone. 



Gelatin is rapidly dissolved in the gastric juice, when it loses the 

 characters by which it is ordinarily recognized and no longer forms a 

 jelly on cooling. This substance is much more rapidly disposed of 

 than the tissues from which it is formed ; and the products of its diges- 

 tion in the gastric juice resemble the substances resulting from the 

 digestion of the albumins. 



Action on Vegetable Nitrogenous Substances. These substances, of 

 which gluten may be taken as the type, are digested to a considerable 

 extent in the stomach. Uncooked gluten is acted on much in the same 

 way as fibrin, and cooked gluten behaves like coagulated albumen. 

 Vegetable articles of food usually contain gluten in greater or less 

 quantity, or substances resembling it, as well as various non-nitrogenous 

 matters and cellulose. The fact that these articles are not easily 

 attacked in any portion of the alimentary canal, unless they have 

 been well comminuted in the mouth, is shown by the passage of grains 

 of corn, beans etc., in the feces. When properly prepared by mastica- 

 tion and insalivation, the action of the gastric juice is to disintegrate 

 them, dissolving out a portion of the nitrogenous matters, freeing starch 

 and other matters so that they may be more easily acted on in the 

 intestines, and leaving the hard indigestible matters, such as cellulose, 

 to pass away in the feces. The nitrogenous constituents of bread are 

 probably acted on in the stomach in the same way and to the same 

 extent as albumins, fibrin and casein. 



Peptones. The peptones in solution form colorless liquids, having 

 a feeble odor resembling that of meat. They are not coagulable by 

 heat or by most acids, a property that distinguishes them from nearly 

 all the nitrogenous constituents of food. They are coagulated, however, 

 by many of the metallic salts, and by chlorin or tannin in slightly 



