CHAPTER XIII 

 MAN AS A HOMOIOTHERMIC ANIMAL 



Man is a mammal and shows greater similarities to 

 anthropoids and other primates than those animals do 

 to other orders of mammals. On the other hand, he 

 shows certain rather striking differences from other pri- 

 mates, but these are largely in degree rather than in 

 kind. His growth in length takes place at a fairly con- 

 stant time rate when his increase in weight takes place 

 at a constant percentage rate. This indicates that *Hhe 

 physiological environment with respect to growth-limit- 

 ing process remains constant" (Brody, 1928). The blood 

 of man is the fluid medium which bathes active living 

 cells, and is remarkably constant in its composition. It 

 contains buffers, rather definite proportions of nutrients 

 and wastes, and various mechanisms for maintaining 

 uniformity. By adding or removing insulation in the 

 form of clothing and by frequenting dwellings man is 

 able during most of his life to live in conditions which 

 are uniform and on the whole conducive to his physio- 

 logical and mental efficiency, and to his peace of mind. 



Stability. — In all habitats and among all groups of 

 the animal kingdom animals seek stability. An animal 

 has better chances of surviving if the environment in 

 which it lives is dependable. Some animals attain this 

 end by living in an environment which is unvarying. 

 Others live in variable environments and vary with them. 



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