CHAPTEE rV. 



ANIMiX NUTEITION. 



I. Formation of Body Tissues. 



62. Formation of tissues. — Since the protein of the food is the 

 sole source of nitrogenous substances in the body, it follows that 

 the formation of flesh is primarily dependent upon the supply of 

 protein in the food. 



In the body there is a slow but continuous breaking down of 

 tissue. The materials which have been dissolved from the food 

 in the process of digestion are absorbed by the blood, and through 

 it distributed to the different parts of the body, where they are 

 either oxidized (consumed), and heat and energy produced, car- 

 bonic acid and water being given off, or are used for the production 

 of components of the body, mainly fat and protein (flesh). The 

 decomposition of nutritive material in the blood, and of muscular 

 and other body tissues, goes on continuously as long as the animal 

 lives, whether it is awake or asleep; being, however, more active 

 in the former condition. The term '' protein consumption" as 

 used in this book is applied to the quantity of nitrogenous 

 materials decomposed in the animal body, whether originating 

 from muscular tissue or nitrogenous nutrients in solution in the 

 fluids of the body. Protein consumption is measured by the 

 amount of nitrogen found in the urine, since practically all the 

 nitrogen which leaves the body passes off through this excre- 

 tion. (57) 



If the nitrogenous wast© results from the destruction of mus- 

 cular tissue, as may be the case during starvation, it is spoken 

 of as "flesh consumption." Since fat-free muscular tissue haa 

 been found to contain, on the average, 3.4 per cent, of nitrogen, 

 the amount of flesh consumed in the body may be found by multi- 



