Influence of Environment 235 



the remarkably adaptive character of all these reactions. Prob- 

 ably the ability to "nerve oneself" to meet emergencies successfully 

 depends upon this secretion. In cases of adrenin-insufficiency 

 there is a lowering of blood pressure, lack of muscular tone and 

 "loss of nerve," such as occur in neurasthenia, "shell shock," etc. 

 On the other hand the secretion of the cortex is said to stimulate 

 the development of the sex glands, and to hasten sexual maturity. 

 Deficiency of this secretion, as in Addison's disease, causes a 

 bronzing of the skin and it has been suggested by Keith that the 

 skin colors of the darker races of mankind are due to a relative 

 deficiency of this secretion, while "we Europeans owe the fairness 

 of our skins to some particular virtue resident in the adrenal 

 bodies." Keith has further suggested that many other racial char- 

 acteristics such as shape and size of head, face, nose, eyes, teeth 

 and lips, length of arms and legs, character and abundance of hair 

 on various parts of the body, etc., may be correlated with the 

 relative activity of the several glands of internal secretion. He 

 believes that in general the white race possesses more of the 

 internal secretions of gonad, thyroid, pituitary and adrenal than 

 do the other races. While these suggestions are highly speculative, 

 they do serve to emphasize the great importance of these secre- 

 tions on the development of body, mind, and personality. 



Since racial characters are inherited it is necessary to assume 

 that in some way the chromosomes of the oosperm influence the 

 development of the glands of internal secretion, and through 

 these, variously bodily and mental characteristics. The influence 

 of the internal secretions on development does not disprove the 

 importance of heredity, but rather it points out a mechanism 

 through which heredity controls development. 



Correlative-Differentiation and Self -Differentiation. Many 

 cases are known in which the development of a part is dependent 

 upon the presence of another part; this is technically known as 

 "correlative differentiation." Thus it has been found that the lens 

 of the eye will develop from any portion of the ectoderm, or outer 



