34 Feeds and Feeding. 



the powers of man. As inert matter takes on the hidden proper- 

 ties of life in plant or animal the problem seems to grow too deep 

 for solution by finite man. Many of th^ changes that occur in the 

 body are known and can be described ; concerning others, but little 

 of a definite nature can be told. 



49. Metabolism. — The processes by which the digested nutrients 

 of the food are utilized for the production of heat and work, or 

 built up into the living matter of the body, in turn being broken 

 down and once more becoming non-living matter, are termed metab- 

 olism. Constructive metabolism, or the building-up processes, is 

 termed anaholism, while the breaking-down and wasting processes 

 are styled cataboUsm. 



50. The circulative canals of the body. — The body of the animal 

 is made up of innumerable cells, which, grouped and modified in 

 myriads of ways, ultimately form all its organs and parts. Every- 

 where among the cells are minute spaces called lymph spaces, which 

 are connected with the lymphatics, a set of vessels which permeate 

 most parts of the body. In some respects the lymphatics resemble 

 the veins, but they are thinner and more transparent and drain in 

 only one direction — toward the heart. Within these vessels is a 

 clear fluid called lymph. These vessels unite with one another, 

 forming a network in many places. Here and there a trunk sub- 

 divides into five or six smaller vessels, and the latter enter a nodule- 

 like body called a lymphatic gland. From this gland come several 

 small vessels, which, after a short space, again unite to form a 

 trunk. Gradually these trunks unite, forming larger trunks until 

 two large ducts are formed which enter a vein in the neck. 



The other set of canals is the arteries and veins, which permeate 

 every portion of the body, the former carrying the blood away 

 from the heart, and the latter carrying it to the heart. At the ex- 

 tremities of the arteries are still more minute tubes, called capil- 

 laries, which connect them with the veins. If one extends his arms 

 in front of him with his finger tips touching, his body will repre- 

 sent the heart, while one arm will represent an artery carrying 

 blood from the heart, and the other a vein conveying blood to the 

 heart. The touching fingers will correspond to the capillaries con- 

 necting the arteries with the veins, and the space all about the fin- 

 gers will represent the surrounding body tissues. In general, neither 

 the veins nor the arteries allow any substance within them to es- 

 cape thru their walls proper. It is thru the capillaries that the nu- 

 tritive matter carried by the blood finds its way into the body tis- 



