140 PHYSIOLOGICAL CHEMISTRY 



may get into the stomach and exert their characteristic activities 

 there. 



The stomach wall is not digested by the gastric juice because 

 the hydrochloric acid cannot pass into the cells of the mucous 

 membrane. These cells also undoubtedly contain anti enzymes 

 which counteract the effect of pepsin, and thus protect the tis- 

 sues. After death however, or if the blood supply to a given 

 area is shut off, the walls of the stomach are attacked and 

 digested. 



Passage of the Food Into the Intestine. The food is carried 

 along the stomach by waves of muscular contraction. The en- 

 trance from, the stomach into the small intestine is guarded by a 

 ring of contractile tissue which is closed ordinarily. When acid 

 comes in contact with the stomach side of this ring, as it does 

 when the food has been thoroughly mixed with gastric juice, the 

 sphincter relaxes and allows a small portion of the stomach con- 

 tents or " chyme" to pass into the small intestine. When this 

 acid mixture comes in contact with the* wall of the small intes- 

 tine, the sphincter closes again. Thus the chyme is passed into 

 the small intestine in small portions. 



Gastric digestion does not complete the disintegration of the 

 foodstuffs. It only starts the process, and prepares the food for 

 further digestion by the enzymes in the intestine. In fact the 

 stomach can be removed without causing death. In such case, 

 only small amounts of food can be taken at a time, and its 

 character must be carefully regulated. 



