100 NUTRITION. 



.o a pulpy fluid called chyme, which varies in its> nature with 

 ths food. Hen.ce the function of the stomach has been 

 named chymification. With this, the function of digestion is 

 complete in many of the lower animals, and chyme is circu- 

 lated throughout the body ; this is the case in Polypi and Jelly- 

 fishes, and some Worms and Mollusks. In other animals, 

 however, the chyme thus formed is transferred to the intes- 

 tine, by a peculiar movement, like that of a worm in creep- 

 ing, which has accordingly received the name of vermicular 

 or peristaltic motion. 



209. The form of the small intestine (i) 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 com- 

 plete 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 res cut of this elaboration is to produce a complete sepa 

 ration of the truly nutritious parts, in the form of a milky 

 ^quid called chyle. The process is called chylification ; and 

 there are great numbers of animals, such as the Insects, 

 Crabs, and Lobsters, some Worms, and most of the Mollusks, 

 in which the product of digestion is not further modified by 

 respiration, but circulates throughout the body as chyle. 



210. The chyle is composed of minute, colorless globules 



of a somewhat flattened form, (Fig. 53.) In 

 the higher animals, the Vertebrates, it is taken 

 up and carried into the blood by means of very 

 minute vessels, called lymphatic . vessels or 

 lacteals, which are distributed every where in 

 the walls of the intestine, and communicate 



