THE DIGESTIVE APPARATUS AND NUTRITION 231 



mass acid. This destroys the ptyalin, and no more starch 

 is converted into sugar. As the saliva acts only upon 

 starch, so the gastric juice acts only upon the proteids. 

 By the muscular movements in the walls of the stomach 

 the food is moved from side to side and thoroughly mixed 

 with the gastric juice, and the mass becomes semifluid. 

 The fats and carbohydrates remain unchanged, except as 

 affected by the warmth of the stomach and by the removal 

 of the proteids which are dissolved out of the mass. 



328. Digestion in the Small Intestine. The food by re 

 maining in the stomach from one hour to three or four, 

 is converted into what is called chyme. The sphincter 

 muscle of the pyloric orifice relaxes at intervals, and the 

 chyme is then passed on into the small intestine by the 

 contractions of the wall of the stomach. Here it soon 

 encounters two other juices, the bile and the pancreatic 

 juice, *>y which it is still further changed. 



329. The Pancreas is a long, slender gland, enlarged at 

 its right end, lying back of the stomach and along its 

 greater curvature, and supported by the mesentery (Fig. 

 94, p. 163). It is pinkish yellow in color, and resembles 

 the salivary glands in structure. A duct runs from one end 

 to the other, joins the common bile duct from the liver, 

 and passes with it obliquely through the wall of the small 

 intestine (Fig. 110). 



330. The Pancreatic Juice. The pancreas has reflex 

 nervous connection with the stomach, and as soon as food 

 enters the latter, secretion begins in the pancreas, and 

 the secreted fluid accumulates in the small intestine. 



The pancreatic juice is a clear, somewhat viscid, alkaline 

 fluid, containing many different substances, the most im- 

 portant being the ferments. Of these there are four. 



One, similar to pepsin, but able to act only in an 



