APPLICATIONS AND POSSIBILITIES 257 



through five epochs that are standard for the normal. The normal 

 is the being who harmonizes with his environment, and yet reacts 

 with it because of recurring needs within him. His endocrine 

 equation settles what is unique and different in him. But the 

 gland which flourishes during the epoch as its time of triumph, 

 when it has its day, determines what makes him like his fellows. 

 From this point of view it becomes permissible to speak of the 

 five Endocrine Epochs. Similarities and resemblances of mind 

 and body between people at a given period of life, childhood, 

 youth, maturity must be put down to their common government 

 by the salient endocrine of the epoch. So one may list: 



Infancy as the epoch of the thymus 



Childhood as the epoch of the pineal 



Adolescence as the epoch of the gonads 



Maturity as the epoch of whatever gland is left in control as the 



result of the life struggle. 

 Senility as the epoch of general endocrine deficiency. 



Infancy as the epoch of the thymus explains why, in any given 

 geographic locality, the babies look alike and act alike. Special- 

 ists in the observation and treatment of infants have noted that 

 not until after the second year is any tendency to differentiation 

 discernible to any extent among them. It is only after the second 

 year, or somewhere around that time, that the child begins to 

 individuate, and distinct individual traits and a personality 

 manifest their outlines. The thymus is the great inhibitor of all 

 the glands of internal secretion. By its checking activity upon 

 the other members of the endocrine system, the thyroid and 

 pituitary in particular, it gives the baby time to grow in bulk, 

 which is its chief business during the first two years of its 

 existence. It quadruples its birth weight. The brain and nervous 

 system complete their growth in mass by the end of the fourth 

 year. Recall the experiments of Gudernatsch working with tad- 

 poles, who showed that feeding with thymus produced giant 

 tadpoles whose metamorphosis into frogs was inhibited, while 

 feeding thyroid produced frogs the size of flies. Differentiation 

 occurred without the preliminary increase in mass usual. As 

 differentiation and bulk thus appear antagonistic, at least at the 

 beginning of growth, the function of the thymus, at a maximum 

 during infancy, seems then to be to restrain the differentiating 

 endocrines, until sufficient material has been accumulated by 

 the organism upon which the differentiating process may work. 



After the second year, the thymus begins to shrink. That is 



