INTESTINAL DIGESTION 279 



Gastric juice also contains, in addition, large amounts 

 of water, ammonium, calcium, potassium, and sodium 

 chlorides; calcium, magnesium, and ferric phosphate 

 are present in small amounts. 



Pepsin converts proteins into peptones. The process 

 is most complicated and, as described by Kiihne in 

 his investigations, is as follows: The protein material 

 is changed first into acid-albumin. If the solution is 

 rendered alkaline, acid albumin will be precipitated. 

 Then the acid albumin is split up into several soluble 

 proteins called, collectively, primary proteoses: albu- 

 mose from albumin, globulose from globulin, etc. The 

 latter in turn take more water and split up into 

 another group of proteins called secondary proteoses or 

 deuteroproteoses. The latter undergo further change 

 and form peptones. 



Rennin curdles cows' milk very rapidly at the body 

 temperature. The casein in the milk is changed from 

 a soluble protein into a solid clot which finally becomes 

 firm and squeezes the whey out of the mass. The curd 

 of cows' milk is a solid clot, whereas the curd of human 

 milk is formed into very fine particles, thus rendering 

 it more digestible to the infants. 



Intestinal Digestion. Upon reaching the small in- 

 testine the chyme containing the partially digested 

 fats, meats, sugars, the peptones, etc., is acted upon 

 by the pancreatic and intestinal juices, and bile, 

 all at the same time; the action of each of these 

 juices will be considered individually. As these 

 partially digested particles are acid in reaction, as 

 they pass through the intestines they cause a reflex 

 stimulation of its cells which pour out an alkaline 

 secretion. 



The Pancreatic Juice. This is secreted by the cells 

 of the glands of the pancreas and reaches the duodenum 

 by way of the pancreatic duct (Wirsung), which opens 

 into the small intestines, together with or ahead of 

 the bile from the liver, and is supposed to be mixed 



