AND PERSONALITY 



it is able to operate a mechanism almost as complicated as 

 that of the Thomson's gazelle. This is evidenced by the fact 

 that the brains and also the thyroid glands of these two 

 animals are of nearly equal weight, as shown in the following 

 comparison: 



Although the brain and the thyroid gland of the sting ray 

 and Thomson's gazelle are of nearly equal weight, the 

 work they do is of unequal value, through the operation of 

 van't HofFs law, that with every degree centigrade of rise 

 in temperature the speed of chemical activity is increased 

 10 per cent. 



We were fortunate in collecting a sloth from the American 

 tropics of the same weight as a salmon from the swift- 

 flowing Restigouche River in Canada. The sloth is one of 

 the most negative of all animals. For inactivity it occupies 

 about the same place in the warm-blooded scale as the 

 alligator does in the cold-blooded scale. It is not possible 

 to compare the intelligence of the warm-blooded sloth and 

 the cold-blooded salmon. Nor is it possible to estimate the 

 portion of the 23-gram brain of the sloth that is required to 

 spark the oxidation needed to maintain its warm-blooded 

 state and its limited intelligence and muscular activity. It 

 is reasonable, however, to think that the greater part of 

 the weight of the brain of the sloth is used to maintain the 

 body temperature. 



In this comparison between the sloth and the salmon we 

 have an excellent example of the fact that the primary role 

 of the brain is to maintain the body temperature, muscular 

 power, and the electric strain necessary to sustain the 



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