160 ANATOMY AND PHYSIOLOGY 



Milk is first acted upon by rennin which sets free the albumin 

 contained and brings out the casein from the caseinogen, in the 

 form of a soft coagulum or curd. Pepsin then transforms both 

 albumin and curd into peptone. 



Clinical Note. The curdled milk which a healthy baby regurgitates is a 

 normal substance; the rennin has acted and it only needs the pepsin to com- 

 plete its digestion. 



The protein of vegetables is digested in the stomach after the 

 cellulose fibers are softened by the acid. Starch may undergo 

 some slight degree of change in the stomach by the action of 

 the saliva which was mixed with it in the mouth, the ptyalin re- 

 maining active until the food becomes acidified. 



Fats are freed from their connective tissue envelopes and float 

 as little globules; they are not digested here (to any great extent 

 this is still uncertain). 



Note. The mineral salts do not require digestion. They are already 

 dissolved in the water for the purpose of entering into combinations in the 

 tissues. The same is true of grape sugar (dextrose). 



When any portion of the stomach contents is Sufficiently pre- 

 pared by gastric digestion, the pyloric sphincter relaxes and the 

 rather thick yellowish fluid called chyme passes through it into the 

 duodenum and thence into the jejunum and ileum. 



Chyme contains partially digested starch and proteins, as well 

 as sugars, peptones, fats, water and mineral salts, gastric juice 

 and some mucus. 



The acidity of the chyme when it reaches the pylorus causes the con- 

 traction of certain muscles of the stomach which open the sphincter and allow 

 the flow of chyme into the duodenum, and thence into the ileum. 



In the intestine the mechanical process is a continuation of the 

 peristaltic movement of the stomach. The circular fibers, by fre- 

 quent constrictions of the tube, divide the mass and force it along, 

 at the same time preventing a too rapid passage. The longitudi- 

 nal fibers assist, by a series of wave-like contractions. 



The chemical process consists in the further digestion of pro- 

 teins, sugars and starch; also the digestion of fats. 



The intestinal fluid is a mixture of intestinal juice, pancre- 

 atic juice and bile, therefore it contains several ferments or 

 enzymes. It is most active in the duodenum. 



