AND PERSONALITY 



weight the greater the facility for cooling, and the greater 

 the facility for heat dissipation the greater the bodily 

 activity a given animal can endure. The great activity 

 of an insect would quickly destroy an elephant. 



An examination of insects with respect to heat elimina- 

 tion shows the insect to have the advantage of a large ratio 

 of body surface to body mass. If, in addition, we take into 

 consideration the added surface area for cooling in the 

 respiratory tubules of the insect, there is a greatly increased 

 facility for heat elimination. Add to this the constant swift 

 flow of air from the wings and from flight, and we see in the 

 insect the most perfect of cooling mechanisms. 



That the metabolism of the muscles of insects is at a high 

 level is obvious from the fact that the wings of a housefly 

 may move 19,800 times in a minute. A large animal would 

 be able to increase the metabolism of its entire body were 

 it ventilated as completely as an insect. 



Since heat elimination occurs only in the lungs and on the 

 surface of an animal, animals were evolved in such a manner 

 that the maximum elimination of heat could be effected. 

 Many expedients were evolved in the process. We see the 

 long legs and the slender bodies of monkeys and of 'man. 

 Evolution took the direction of cooling, not only by means 

 of the absorption of heat by colder water and colder air, but 

 equally by evaporation of water by the cooling device of 

 sweating. In man evolution set up a mechanism by which 

 much of the blood from the warmer internal part could be 

 shifted by dilation of the blood vessels in the skin, thus 

 further facilitating the loss of heat, and in certain hunting 

 animals, such as the dog and the wolf, evolution seized 

 upon rapid respiration and upon the large moist surface of 

 the tongue as an additional means for facilitating the loss of 

 heat. 



So fundamental is this balance between the production of 

 energy and the elimination of heat that evolution adapted 

 animals of larger size to spend much time in the water, in 



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