THE ANIMAL BODY DIGESTION METABOLISM 33 



57. Metabolism. The changes which the digested and absorbed nutri- 

 ents undergo within the body in their use for various purposes are termed 

 metabolism. As is discussed in detail in the following chapters, the nu- 

 trients may be built up into the living matter of the body, or they may be 

 broken down in the production of heat and work. Constructive metab- 

 olism, or the building-up processes, is termed anabolism, while the 

 breaking-down and wasting processes are called catabolism. 



58. The circulative canals of the body. The body of the animal is 

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



DIAGRAM OP THE CIRCULATION OF THE BLOOD 



1. The heart; 2, artery carrying blood to the head and fore limbs; 3, circula- 

 tion thru the upper portion of the body; 4, vein carrying blood from upper part 

 of body back to the heart; 5, artery carrying venous blood to lungs; 6, circula- 

 tion thru lungs; 7, vein carrying arterial blood back to heart; 8, artery carrying 

 blood to lower portion of body; 9, circulation thru rear extremities; 10, vein 

 carrying blood to heart from rear extremities; 11, artery carrying blood to in- 

 testines; 12, circulation thru intestinal capillaries; 13, portal vein carrying 

 blood to liver; 14, circulation thru liver; 15, circulation thru kidneys. (From 

 Smith, "Manual of Veterinary Physiology.") 



of ways, ultimately form all its organs and parts. Everywhere among 

 the cells are minute spaces called lymph spaces, which are connected 

 with the lymphatics, a set of vessels which permeate the various tissues 

 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 subdivides 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 a 

 large duct and another smaller one are formed which enter veins in the 

 neck. 



The arteries and veins form the other set of canals. These 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 extremities of the 

 arteries are still more minute tubes, called capillaries, which connect them 



