AND PERSONALITY 



infinite numbers or combinations of patterns of action, each 

 of which must be executed by brain cells that supply the 

 energy for thinking, for the expression of the emotions, and 

 for the vast number of muscular acts performed by civilized 

 man. 



An analogy to civilized man's requirement of a large 

 brain for the execution of the many separate acts that he 

 performs was seen in the size of the brain of the sting ray 

 that we collected at Key West. The sting ray has ninety- 

 four pairs of muscles that must coordinate and contract 

 rhythmically in many vicissitudes of orientation on the 

 shallow, sandy beaches. In the sting ray the brain is accord- 

 ingly relatively larger than that seen in any other fish or 

 reptile, since in the brain of the sting ray there must exist 

 not only the patterns of action of the ninety-four pairs of 

 muscles but also the necessary number of brain cells to 

 execute these patterns of action. 



This conception explains the large size of the brain 

 of man compared with that of the ape and the large 

 size of the brain of civilized man, whose thinking brain 

 drives his hands and the feet so continuously in the 

 operation of the web of life, compared with that of native 

 man. 



The fourth biological principle, that in man the brain 

 and the thyroid gland rose together, has been clearly 

 established in our long study of the energy-controlling 

 organs of the various species of animals and in certain 

 racial studies of man. 



The thyroid hormone controls the rate of oxidation in 

 the billions of brain cells, including the ceils of the center 

 that sends impulses over the sympathetic nerves to the 

 celiac ganglia and plexuses and adrenal glands, thus indi- 

 rectly controlling the force and frequency of the heartbeat 

 and, in consequence, the electric potential of the entire 

 organism. Therefore, the thyroid gland may be considered to 

 exert adaptive control of oxidation in the entire organism. 



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