DIGESTION AND THE DIGESTIVE AGENTS. 337 



Sixth. The milk has been curdled by the acid of the 

 stomach and by the rennin, and more or less fully converted 

 into peptones by the pepsin. 



Seventh. A number of mineral salts which we take into 

 the body daily, as ashy ingredients of our foods, have been 

 dissolved by the acid of the stomach and so enabled to 

 pass into the blood. In this way much of the mineral mat- 

 ter for the body, which would be perfectly insoluble in water 

 is dissolved, and so rendered suitable for the body's pur- 

 poses. With the gastric contents in this condition the py- 

 loric sphincter from time to time relaxes, and the now 

 fairly semi-liquid food is passed into the duodenum to be 

 further subjected to the action of the succeeding digestive 

 agents. 



The explanation why the stomach does not digest itself 

 is given by some as due to the resistance of its epithelial 

 lining, by means of which it is protected from the digestive 

 action of the juice, the keratin of the epithelium cells being 

 indigestible. Others find the explanation in the circulating 

 alkaline blood through the walls, by means of which the 

 walls themselves can never become acid, and so never sus- 

 ceptible to the action of the gastric juice. It is interesting 

 to note that ulcerations of the mucous membrane become 

 susceptible to self-digestion, which may finally lead to the 

 formation of holes through the gastric wall. 



3. The Pancreatic Juice. Fresh pancreatic juice is a 

 clear, viscid, alkaline, rapidly putrefying liquid, slightly 

 heavier than water, coagulating completely when subjected 

 to boiling. Its composition is as follows: 



First, albumens. Just what the exact nature of these 

 albumens is has not yet been determined. They coagulate 

 easily upon being boiled. Whether, in fact, they have any 

 digestive action at all is still questionable. 



Second, several ferments or enzymes. These enzymes 

 are trypsin, amylopsin, and steapsin. 



Third, a number of mineral salts, mostly sodium salts. 



Fourth, water. 

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