284 THE GLANDS REGULATING PERSONALITY 



ances in the mother during pregnancy. Pregnant animals fed on 

 thyroid give birth to young with large thymus glands. The diet 

 of the mother has been proved conclusively to influence the 

 development and constitution of the child. As the internal 

 secretions influence the history of the food in the body, they 

 affect development in the womb indirectly as well as directly. 

 Certainly, whether or no we learn how to change the nature of 

 germplasm within a short time, we have in the endocrines the 

 means at hand for affecting the whole individual that is born 

 and sees the light of day. 



The Control of Mutations 



The true physical and intellectual evolution of man depends 

 upon the production of mutations of a desirable kind that can 

 survive. The information furnished by the study of the en- 

 docrines concerning the genesis of personality provides the foun- 

 dations for a positive eugenics, a eugenics of the encouragement 

 of desirable matings, with the proper legal and social procedures. 

 Selective breeding for the production of the best endocrine types 

 should become practicable. 



But the biologist should be able to go farther. If the 

 eugenist is to limit himself to the method of the animal breeder 

 he will have to rest satisfied with the characters or hereditary 

 factors given, that turn up spontaneously in an individual. But 

 with the internal secretions as the controllable controllers of mu- 

 tations, the outlook changes. It should become possible to pro- 

 duce new mutations, good and bad, to speed up their production 

 at any rate. The feeding of thyroid to a gifted father before 

 procreation might enhance immeasurably the chances of trans- 

 mission of his gift as well as of its intensification in his offspring. 

 A field of investigation is opened that would embrace in due time 

 the deliberate control of human evolution. 



All the physical traits, stature, color, muscle function, and so 



on, ofiVr themselves for improvement, as well ai and 



intellectual and emotional factors which have dominated 



n's social evolution. Th( ous dis- 



orders in civilised count !l i'» the nervous infante 



•ialist in children's diseases is called upon to treat, shows 

 that the nervous system of tin of mankind is in a 



state of unstable equilibrium I ! tne 



mi a of the En- 



