52 THE GLANDS REGULATING PERSONALITY 



length of time a single administration of thyroxin functions with- 

 in the body is about three weeks. Again we have occasion to 

 notice a protective device of the cells. Since the presence of 

 thyroxin in the tissues determines the rate at which they burn 

 themselves up, it is obvious that if there were no mechanism 

 for retarding its action, and at need varying it, they really would 

 set fire to themselves. That is to say, if the tissues held a 

 maximum of the thyroid internal secretion, and had to take up 

 more and more as it was fed out to them by the thyroid through 

 the blood, the pressure of energy production would attain the 

 state of a boiler without a safety valve. Even if self-destruction 

 were avoided by the ingestion of the largest quantities of energy- 

 bearing foods, rest for the cells would be difficult, if not impos- 

 sible. 



The thyroxin in the tissues diminishes after a period of great 

 exertion, the thyroxin probably being carried back to the thyroid 

 gland and kept there as reserve until further demand. So it has 

 been discovered that during the winter months, the thyroid glands 

 of beef, sheep and hogs all contain much less iodine than during 

 the summer months. During the winter months, manifestly, more 

 energy is required to maintain body temperature, hence the gland 

 surrenders more of its secretion to the tissues and so keeps less 

 • of it itself. There must be, too, a certain wearing out of the 

 potency of the iodine with time. Even dead inorganic catalysts, 

 made of simple elements, wear out after having been used time 

 and time again. 



Though the thyroid is the supreme energizer, life is incom- 

 patible with a certain excess of it. Death can be produced by 

 successive daily injections of its internal secretion. But it has, 

 besides the energizing effect, certain formative and nervous influ- 

 ences equally marvelous. As illustrations, there are the cases of 

 thyroid deprivation in human beings, cretinism and myxedema, 

 as well as those in which it is believed there occurs an excess of 

 the thyroid secretion in the blood and tissues, the condition of 

 /it/pcrthyroidism. 



Cretinism as Thyroid Deficiency 



Not that there is any arresting contrast of startling difference 

 between the phenomena presented by different species. The 

 younger the animal, the grosser the morbid symptoms witnessed. 

 The animal fails to grow. The bones and cartilage, except of 



