76 



NUTRITION. 



is transferred to the intestine, by a peculiar movement like 

 that of a worm in creeping, which has accordingly received 

 the name of vermicular or peristaltic motion. 



209. The form of the small intestine is less variable than 

 that of the stomach. It is a narrow tube with thin walls, 

 coiled in various directions in the vertebrate animals, but 

 more simple in the invertebrates, especially the insects. Its 

 length varies according to the nature of the food, being in 

 general longer in herbivorous than in carnivorous animals. 

 In this portion of the canal, the aliment undergoes its 

 complete elaboration, through the agency of certain juices 

 which here mingle with the chyme, such as the bile secreted 

 by the liver, and the pancreatic juice secreted by the 

 pancreas. The result of this elaboration is to produce a 

 complete separation of the truly nutritious parts, in the 

 form of a milky liquid called chyle. The process is called 

 chylification. 



210. The chyle is composed of minute, colorless globules, 



of a somewhat flattened form (Fig. 53). It 

 is taken up and carried into the blood by 

 means of very minute vessels, called lym- 

 \phatic vessels or lacteals, which are distri- 

 buted everywhere in the walls of the intestine, 

 and communicate with the veins, forming also 

 in their course several glandu- 

 lar masses, as seen on the por- 

 tion of intestine connected with a 

 vein (Fig. 54). The residue 

 passes on to the large intestine, 

 from whence it is expelled in 

 the form of excrement. 



211. These organs constitute 

 the essential apparatus for diges- 

 . 54. tion ; but there are, in the higher 



animals, several additional ones for aiding in the reduction of 



Fig. 53. 



