212 



ELEMENTS OF PHYSIOLOGY 



376. The Peristalsis of the Stomach. Anything taken 

 into the stomach causes wavelike contractions in its mus- 

 cular walls. The food is caused to go from the gullet to 

 the left of the cardiac orifice, then down to the right and 

 back again, the circuit from left to right, then from right to 

 left, taking from one to three minutes, according to the 



activity of the peristalsis. The 

 muscular fibers in the walls of the 

 stomach are in three layers (Fig. 

 169); one layer runs lengthwise, 

 another around, and the third 

 obliquely, so that the varied con- 

 tractions cause the food to become 

 thoroughly mixed with the 



377. Gastric Juice. This is a 

 yellowish fluid and consists of 

 water, having in solution hydro- 

 chloric acid and two ferments. 

 These remarkable substances, 

 although existing in very small 

 quantities, are able to change the 

 composition of large quantities of 

 food. In times of rest, when there 

 is no food present, the mucous mem- 

 brane of the stomach is of a pale 

 red color. But when food is intro- 

 duced, a change at once takes 

 place. The membrane becomes 



charged with blood and consequently turns to a deep red 

 color. The gastric juice, secreted by many small glands 

 (Fig. 168), appears on the walls of the stomach, and peri- 

 staltic action begins (Fig. 169). 



378. The ferment of the gastric juice called rennin acts 

 by coagulating milk, a change somewhat like the coagula- 

 tion of the blood. It causes coagulation by acting upon 



FIG. 168. Three Glands of 

 the Stomach. 



t, epithelium at inner surface of 

 stomach; m, mouth of gland; 

 /, principal cells of gland; ov, 

 ovoid cells; c, connective tissue 

 below and between the glands. 



