260 THE GLANDS REGULATING PERSONALITY 



senility returns. It is as if a storage battery, recharged, runs 

 down and becomes dead again. Slitting the genital duct of the 

 other testis, causing its interstitial cells to hypertrophy and mul- 

 tiply, repeats the effects of the first experiment. The organism 

 responds again to the new waves of vitality that vibrate through 

 it. That it is recharged is demonstrated again by a revival of 

 sex appetite and sex activity. The female which had become an 

 object of indifference is reinstated as a creature to be sought and 

 pursued. The second period ends in its turn. And now entirely 

 new interstitial glands, in the form of fresh testes removed from 

 a young animal, are transplanted into the body of the old rat. 

 Once more youth returns. But now it burns itself more quickly 

 than even before. An acute exhaustion of the mind appears 

 first. Then all the other phenomena of old age steal back upon 

 the old rat, and senility, firmly established in the saddle, rides 

 him to the end. 



The Possibilities of Rejuvenation 



Whatever other deductions may be extracted from these experi- 

 ments, they prove beyond a doubt the existence of an endocrine 

 factor in the process of aging, as well as an arterial. They also 

 demonstrate that the internal secretion of the sex glands, well 

 advertised as it has been as the Elixir of Youth that Ponce de 

 Leon, and Brown-Sequard with so many others, pursued in vain, 

 is not the whole story. For if it was, the duration of the new 

 youth should be another span of life, whereas in actuality it is 

 only a fraction of that time. This fact, together with a number 

 of others, make clear that while the gonads may be the jeune 

 premier of the drama, the vitality of the plot depends upon the 

 other endocrines. Since old age is an exhaustion, permanent and 

 irreparable of all the members of the ductless gland directorate, 

 the reason becomes clear for the te mp orary quality of the re- 

 juvenation effected by the procedures of Steinaeh. 



Practically, then, the question at once arises: which of the 

 glands in particular are involved? There ll fn>t (hat ubiquitous 

 agent in I the thyroid. Cheinieal analysis of r 



the iodine content deere—M with the age of the 

 individual, and becomes specially low after forty. It is 



•neoopause in women thai myxedema, the di aea a e of com- 

 plete degeneration of the thyroid, and of the pi id mental 

 is most frequ< at l oid of old p< 



