STOMACH DIGESTION 69 



89. Peristalsis of the stomach. Anything taken into 

 the stomach causes a continuous and regular movement 

 of the organ, due to the alternate contraction and relax- 

 ation of its muscular fibers. This is an example of slow 

 peristalsis. The food is thus caused to flow in a steady 

 stream from the esophagus to the left, and then down to 

 the right and back again, completing the circuit of the 

 stomach in about three minutes. By this movement it is 

 thoroughly mixed with the gastric juice. 



90. Ferments of the gastric juice. One of the ferments 

 of the gastric juice, rennin, acts by coagulating milk. In 

 the child this action is very important. 



The other ferment, pepsin, softens the albumin of food 

 and changes its character so that it will dissolve in water 

 and diffuse through the walls of the blood tubes to become 

 a part of the blood. This form of albumin is called peptone. 



A quarter of a grain of pepsin can render a whole white of an egg 

 soluble. It acts best at the temperature of the body, and there must 

 be an acid present. The surface of the food particles are acted upon 

 first, and the products of its action are rubbed off by the peristalsis of 

 the stomach, and the next layer is acted upon in the same manner. 

 Some of the gastric juice penetrates between the particles of food, and 

 slowly eats its way into the food mass, thus dissolving apart the sepa- 

 rate cells which compose the food. Its action is confined solely to the 

 albumin. In fat meat the albuminous pockets are eaten away, and the 

 fat is set free. Starch is not acted upon, except to be freed from its 

 albuminous envelopes. 



The result of stomach digestion is a fluid called chyme. 

 Peptone imparts to it a bitter taste, while small particles 

 of fat give it a milky appearance. Food then appears as 

 it would if it had been boiled for a long time. 



fc 



91. Use of the acid. Pepsin can act only in the presence of 

 acid, in an amount at least sufficient to neutralize the alkali always 



