216 



COMPOSITION OF CHYME. 



digested, partly digested, and undigested materials. Some of 

 the starch has been changed to sugar, but only a small part, 

 owing to the short time of mastication. (It is believed that 

 the slower mastication in the herbivora changes much more of 

 the starch to sugar.) 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 move- 

 ments 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 

 indigestible substances. At intervals the sphincter muscles 



of the pylorus relax, and the con- 

 tractions of the stomach send the 

 liquid mixture into the intestines 

 by spurts. 



The Intestine. The small 

 intestine has essentially the same 

 structure as the parts of the diges- 

 tive tube already studied, namely, 

 a mucous lining beset with an im- 

 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 intestines have also the mus- 

 cular coats, about as described. And the muscular coat has 



Fig. 62. Horizontal Section 



through the Mucous Membrane of 



the Intestine, showing Intestinal 



Glands In Transverse Section. 



(Highly Magnified.') 



