PHYSIOLOGY. 



digested materials. Some of the starch has been changed 

 to sugar, but only a small part, owing to the short time of 

 mastication. The bulk of the starch is unchanged. Some 

 of the proteid is already changed to peptone. Part is still 

 proteid, while part is in an intermediate stage between 

 proteid and peptone. Fat is essentially unchanged, but is 

 melted by the heat of the mouth and stomach, and is more 

 or less divided into small drops by mastication and the 

 movements of the stomach. For instance, in eating bread 

 and butter, the melting butter will be finely mixed with the 

 bread as it is chewed. The water in the chyme was partly 

 taken as such, and partly derived from the saliva and 

 gastric juice. There are also present ptyalin, pepsin, 



mucus, salts, and some indigesti- 

 ble substances. At intervals the 

 sphincter muscles of the pylorus 

 relax, and the contractions of the 

 stomach send the liquid mixture 

 into the intestines by spurts. 



The Intestine. The small in- 

 testine has essentially the same 

 structure as the parts of the diges- 



Fig. 62. Horizontal Section A . , , . ,. , , 



through the MUCOUS Membrane of tive tube already studied, namely, 



the Intestine, showing Intestinal a mUCOUS lining beset with an im- 



Glands in Transverse Section. 



(Highly Magnified.) mense number of tubular glands, 



called intestinal glands. These 



secrete a liquid collectively called the intestinal juice, whose 

 exact work is not well known, but which may be said to 

 complete the work of the other secretions. The intestine 

 has also a muscular coat with circular and longitudinal 

 fibers. And the muscular coat does the same work of 

 mixing the juices with the food and of moving it along. 



