134 



BIOLOGY AND HUMAN LIFE 



a short distance at a time. This movement is called peristalsis 

 and is similar to the swallowing movement of the gullet. In 

 vomiting, this peristaltic action of the food tube is reversed. 

 Neither the saliva ferments nor the gastric ferments have any 

 effect upon fats. When a food mixture passes from the stomach, 



it contains all the sugar 

 that was there to begin 

 with, all the sugar that 

 was formed by the di- 

 gestive action of the 

 saliva, and whatever 

 starch was not digested. 

 It contains the peptones 

 resulting from the gas- 

 tric digestion, and par- 

 ticles of proteins that 

 were not digested. In 

 addition there is a 

 quantity of water, min- 

 eral salts, the remains 

 of the gastric and sali- 

 vary juices, and the 

 fibers and cell walls of 

 the food material. In 

 the intestines further 



Fig. 76. Glands of the stomach 



The gastric juice ispoured into the stomach through 

 tubes, a, which are lined by a layer of delicate 

 cells; it is produced by special gland cells, b, from 

 materials brought by the blood in fine vessels, c. 

 The stomach juice contains, in addition to an acid, 

 a special ferment, pepsin. In the presence of acids 

 pepsin acts upon proteins and changes them into 

 soluble peptones 



changes take place. 



Near the beginning of the intestine two small tubes, or ducts 

 {h, i, Fig. 74), empty at a common opening. One of them leads 

 from the largest gland in the body, the liver ; the other from 

 another important gland, the pancreas (see 0, Fig. 74). 



112. The pancreas. The juice secreted by the pancreas con- 

 tains three important kinds of ferments : 



1. A ferment that converts starch into sugar. 



2. A ferment that digests proteins into simpler compounds. 

 Any starch that has been swallowed before the saliva has had 



time to transform it into sugar, and any protein that has passed 



