INTELLIGENCE, POWER, 



plasm that is exquisitely sensitive to all stimuli, is easily 

 disintegrated by heat, and is the mechanism by which heat- 

 stroke is produced. 



Animals take into their bodies large amounts of solar 

 energy in the form of plant food or the flesh of other ani- 

 mals. This energy constitutes a liability as well as an asset, 

 for the nitro fraction thus taken in the food is the fraction 

 of protoplasm that governs the chemical decomposition that 

 leads to heatstroke. Added to the heat produced by this 

 continuous disintegration is that produced by the oxida- 

 tion induced by the brain and controlled by the thyroid 

 and adrenal glands. It is clear, then, that each animal 

 could be provided with only as large a brain, heart, volume 

 of blood, thyroid gland, and adrenal-sympathetic system 

 as would maintain the body temperature at a safe level 

 below heatstroke. 



The level of heatstroke, however, is not dependent alone 

 upon the size of the brain, the heart, the volume of blood, 

 the thyroid gland, and the adrenal-sympathetic system, 

 that is, it is not dependent solely upon metabolism. It is 

 also dependent upon the facility for cooling, which, in turn, 

 depends on the size of the animal, the presence of sweat 

 glands, fur, thickness and vascularization of the skin, and 

 the size of the lungs. 



The ratio of the surface of a small animal to its weight is 

 greater than the ratio of the surface of a large animal to its 

 weight. Consider the mouse and the elephant. The mouse 

 and the elephant exist at different levels of oxidation 

 per unit of surface. Therefore, not only does the relative 

 size of the organs that control the rate of oxidation in these 

 two animals prevent rapid disintegration of protoplasm 

 under excess heat, but also and equally it controls the 

 facility for cooling the animal. In animals, just as in motors, 

 not only is combustion essential, but so also is the cooling 

 system. Since the loss of heat in animals is essentially at the 

 surface, the greater the ratio of the surface to the body 



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