NUTRITION PROPER. 



313 



the appearance of pea soup, and called chyme. This is 

 passed on to the intestines, to undergo the next stage. 



Chemical Work ; Peptonization. — The gastric 

 juice is elaborated by the whole mucous membrane of 

 the stomach, but especially by the peptic glands. 

 Glands, as already explained (page 294), are a device for 

 increasing the extent of the epithelial surface. In this 

 case the device is of the simplest sort. The interior of 

 the stomach is thickly strewed with deep pits lined with 



Fig iqq— A, interior of stomach, showing the openings of the peptic 

 ' glands ; B, section through the walls. 



epithelium (Fig. 199). Some of these pitlike tubes are 

 branched, but only simply. The epithelial surface is 

 thus many times greater than the interior surface of 

 the stomach. The gastric juice is secreted mainly in 

 these pits, both simple and branched. As soon as the 

 food touches the stomach the mucous membrane be- 

 comes engorged with blood and reddened, and the gas- 

 tric secretion commences. 



