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 expression of the blending action of the different internal secretions.  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 percentages of the pigments in each particular skin, can be determined by means of a rotating disc.  Thus a white person’s skin may have the following composition: 

Black 8% Red 50%

Yellow 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 hyperthyroid and the subadrenal is soft and moist, because of their antagonistic effects upon the sympathetic system.  The subthyroid 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 secretion 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.  The latter occurs most regularly in the subadrenal types, the former in the hyperthyroid.  Both forms of reaction run parallel to the different check or drive effects of the vegetative apparatus.  With too much drive, that is, too much thyroid, there is the flushing reaction; with too little check, that is, with too little adrenal, there is the whitening.  These differences probably explain the emotional reactions of the face.  In anger, for example, some people become a dead white, others a fiery red.  Whether one will do one or the other may depend upon the relative predominance of the thyroid or of adrenal in the individual.