CHAPTER IX 



THE DISTRIBUTION AND USE OF THE 

 DIGESTED FOOD 



The digested food, after absorption, ajl passes into 

 the blood, either directly or indirectly, and mixes with 

 it. The materials which are to serve the purposes of 

 nutrition are now taken up by a stream of liquid that is 

 in constant motion through the minutest divisions of 

 every part of the animal. Flowing in regular channels 

 the blood reaches not only the bones and muscular tis- 

 sues, but it passes through several special organs and 

 glands where the nutrients it is carrying and certain of 

 its own constituents meet with profound changes. It is 

 here that we discover the manner in which food is applied 

 • to use and what are some of the transformations which, 

 the proteins, carbohydrates, and fats imdergo in perform- 

 ing their functions. 



In order to follow intelligently this most interesting 

 phase of nutrition, we must know something of the blood 

 and of the organs — ^the limgs, liver, and kidneys — ^through 

 which it passes. 



199. The blood. — The blood, which makes up from 

 3 to 4 per cent of the total weight of the live animal, 

 when in a fresh state, is apparently colored and opaque, 

 but if a minute portion is examined with a microscope, it 

 is seen to be a comparatively clear liquid in which float 

 numerous reddish disk-like bodies. These bodies, which 

 are known as corpuscles, give to the blood its bright red 



(138) 



