xi FOODS IN THE TISSUES 147 



that leave the body, as the exhaled air, the sweat, and 

 the material excreted from the kidneys and bowels, 

 carry with them a large amount of heat. 



112. Regulation of Temperature. Some animals take 

 on the temperature of the medium in which they live. 

 If you place a frog, a lizard, or a fish in cold water for 

 some time, its blood will be nearly as cold as the water. 

 Should you raise the temperature of the water slowly, 

 they would adapt themselves to great changes. The 

 temperature of their blood depends upon and is regu- 

 lated by their environment. Such animals are said to 

 be cold blooded. 



In man and the higher animals the production and 

 loss of heat are controlled by the nervous system. The 

 skin is the important regulator of the loss of heat. 

 When the pores of the skin are open and the sweat 

 glands are busily at work, a large amount of heat may 

 be lost by perspiration. Again, the capillaries of the 

 skin may dilate and expose a large amount of blood to 

 the surface of the body, from which heat will radiate 

 rapidly. All this is controlled by the nerves of the 

 skin. 



The kind and amount of clothing we wear are impor- 

 tant factors in regulating the loss of heat from the skin. 



SUMMARY OF THE MAIN POINTS 



1. Lymph is blood without red corpuscles. It contains all 

 the foods and wastes of the cells. 



2. Albumins are the building and repairing foods. No 

 growth occurs without them. They are also oxidized. 



