THE DIGESTIVE SYSTEM 165 



quantity. The pepsin is associated with the enzymes of 

 the secretions. Besides pepsin, a second ferment, termed 

 rennin, exists in the gastric juice, which has the power of 

 coagulating the caseinogen of milk. By this action the 

 caseinogen is split into insoluble casein and soluble albu- 

 min. Calcium phosphate is essential to the action of this 

 enzyme (Brubaker). 



The gastric glands are embedded within the mucous 

 membrane in enormous numbers. They are tubular in 

 character, as may be seen in Fig. 82, which represents the 

 circulation within the glands, as well as the tubules and 

 absorbent radicals. 



The principal action of the gastric juice is to transform 

 the different proteid principles of the food into peptones, 

 which is due to the hydrochloric acid and pepsin; when the 

 albumins come in relation with the acid they are converted 

 into parapeptones, and in a short period of time they are 

 converted into albuminose with the aid of pepsin ; finally, 

 they are converted into peptones and absorbed. 



THE INTESTINES 



The small intestine is the narrowest part of the 

 digestive tract, occupying the central and lower parts of 

 the abdominal and pelvic cavities. It is about 25 feet 

 in length, and is divided, for descriptive purposes, into 

 three parts the duodenum, jejunum, and ileum. It 

 is suspended from the spine by a fold of peritoneum 

 called the mesentery. 



The large intestine extends from the ileum to the 

 anus, and is about 5 feet in length, and is also divided, for 

 purposes of description, into three parts the cecum, colon, 

 and rectum. 



The Small Intestine. The Duodenum. This por- 

 tion is somewhat greater in diameter than the remainder 

 of the small intestine. It received its name from the fact 



