278 DIGESTION 



agus during deglutition or swallowing. The stomach 

 receives the food, whereupon the muscular fibers 

 of the cardiac and pyloric orifices close by a sphincter- 

 like contraction. The food is held within the stomach 

 for a few moments, then is turned over and over and 

 moulded by the muscular contractions of the stomach 

 until it is reduced to a liquid or semiliquid consist- 

 ency called chyme, by the action of the gastric juice. 

 The pyloric portion of the stomach becomes shaped 

 like a tube, and the fundus or most dilated portion of 

 the stomach contracts and forces the food (chyme) 

 into the duodenum, where it is conveyed by a similar 

 peristaltic contraction of its walls into the small 

 intestine. There is no given time for emptying the 

 stomach. As the food is liquefied it is forced out of 

 the stomach and then the semisolid particles of the 

 diet which are not digested by gastric juice are passed 

 from the stomach, leaving it empty except for the 

 alkaline secretion which is mucous, and protects its 

 walls. Digestion in the stomach lasts from two to 

 five hours, depending upon the food, quantity and 

 quality, pathologic conditions, etc. No nourishment 

 is absorbed by the lymph or bloodvessels of the 

 stomach. 



Gastric Juice. Under normal physiologic conditions 

 gastric juice is a thin, almost colorless liquid, with a 

 characteristic odor and acid reaction. The average 

 of acidity varies; normally it is 0.02 per cent. The 

 acidity is due to the presence of hydrochloric acid, 

 and in certain conditions of health and disease, lactic 

 acid may be found. As a result of disease, the acidity 

 may be increased, decreased, or entirely absent. The 

 gastric juice contains in addition to the above, pepsin 

 and rennin, two proteolytic ferments or enzymes; the 

 former is active only in an acid medium, and the 

 latter is the ferment which curdles milk or divides 

 it into a solid portion, casein, and the liquid portion, 

 whey. The chemic nature of these enzymes is unknown. 



