HOW GLANDS INFLUENCE THE NORMAL BODY 125 



The Skin 



The skin is influenced in its color, moisture, hairiness, texture, 

 fat content and disease vulnerability by the endocrines. The 

 question of color is very interesting, for it is probably the ex- 

 pression of the blending action of the different internal secre- 

 tions. Davenport, the American student of heredity and 

 eugenics, has shown that neither white nor black skins are either 

 perfectly white or perfectly black, but are mixtures in various 

 proportions of black, yellow, red and white. The exact per- 

 centages of the pigments in each particular skin, can be deter- 

 mined by means of a rotating disc. Thus a white person's skin 

 may have the following composition: 



Black >t. . . 8% Red 50% 



Yellow sh. . . . 9% White 33% 



The composition of the skin of a very black negro may be: 



Black 68% Red 26% 



Yellow :._,. 2% White 7% 



Now the fact that in Addison's disease in which the adrenals 

 are destroyed there occurs a coincident increase in the black in 

 the skin, and other evidence pointing to adrenal implication in 

 dark complexioned white people, as well as in those possessing 

 pigmented spots, seems to indicate the adrenals as controllers of 

 the black and white factors. Davenport has concluded that there 

 are two double factors for black pigmentation in the full-blooded 

 negro which are separately inheritable. The determinants of 

 the red and yellow have still to be worked out. 



The moistness of the skin, as perspiration, depends upon the 

 number and activity of the sweat glands. It varies with the 

 water content of the body, the state of the vegetative nervous 

 system, and the body temperature. Thus the skin of the hyper- 

 thyroid and the subadrenal is soft and moist, because of their 

 antagonistic effects upon the sympathetic system. The sub- 

 thyroid and the hyperadrenal have dry and harsh skins for the 

 same reason, if no other glands intervene. However, in both of 

 the latter, if there is a persistent thymus, the skin will retain 

 the bland quality of adolescence. 



There is a curious variation among the different internal secre- 

 tion types in the reaction of the skin to stroking. When the 

 skin, especially the skin over the shoulders, the breasts and the 

 abdomen, is stroked with some blunt object, the blood vessels 

 react either by a greater filling up or emptying of themselves. 



