THE (ESOPHAGUS AND STOMACH 



103 



in a dissolved form by thoroughly washing the mucous membrane 

 of the stomach of any animal with water ; or it may be procured 

 in the solid form from the chemist. The power of pepsin as 

 a digestive fluid may be illustrated by the following experi- 

 ment : 



Cut up a little lean meat into very small pieces, thus imitating mastication. 

 Put them into a vessel with some water, 

 a little pepsin, and a drop or two of 

 hydrochloric acid. Heat this mixture 

 up to a temperature of 1 00 F. (the 

 temperature of the body), and keep it 

 at this for a few hours, stirring fre- 

 quently with a glass rod to imitate the 

 motions in the stomach. The meat 

 thus treated will be reduced to a pulp 

 as in the stomach. 



The gastric fluid has no 

 action on starchy foods, neither 

 does it act on fats. The former, 

 however, are dissolved in the 

 stomach by the swallowed saliva, 

 but the acidity of the gastric 

 juice somewhat retards this 

 action. Fatty tissue consists of 

 fat cells united together by areo- 

 lar tissue, and each cell consists 

 of a particle of fat surrounded 

 by a cell-wall of albuminous 

 (nitrogenous) substance. Con- 

 sequently, when fatty tissue 

 passes into the stomach, the 

 areolar tissue and the albumi- 

 nous cell-walls are dissolved, and 

 the fat itself is set free in the 

 form of minute globules, giving 

 the whole contents of the sto- 

 mach a milky appearance. 



Fig. 101. Peptic Gland from the 

 Mucous Membrane of the Sto- 

 mach. Highly magnified 



This milky fluid is called chyme (Gr. cheo, I pour) because it 

 is poured into the intestine. It consists of 



(a) Saliva and partially dissolved starchy foods. 



(b) Gastric fluid and partially dissolved nitrogenous foods. 



(c) Undigested fat in the form of minute globules. 



(d) Mucus from the mucous glands. 



(e) Indigestible substances. 



The character of the chyme varies considerably according to 



