The pigment is not uniformly distributed, as I have said, through the whole body, and this is so with the Whites as well as with the darkest races. In all of them the parts of the body most deeply coloured are the nape of the neck, the back (as with animals), the back part of the limbs, the arm-pits, the scrotum, and the breasts; the belly (as with animals), the insides of the hands, the soles of the feet, are among the most lightly coloured. The parts covered by garments are less coloured among white and yellow races than the parts uncovered; it is affirmed, but without reliable proofs, that the contrary takes place among the dark and black populations.
In the iris, the pigmentation assumes a particular character. As we know, this perforated diaphragm of the eye is composed, histologically, of three layers: an anterior epithelial one; a middle one, the “stroma,” with muscular fibres, designed to enlarge or reduce the pupil; and lastly, a posterior layer, called the pigmental layer. But it must not be thought that this layer is the only repository of the pigment of the iris. It is also found accumulated in the thickness of the stroma, and between the muscular fibres. In both places the granules of the pigment have the same brown colour as in the rest of the body, but the pigment of the posterior or pigmental layer is only seen through the stroma and appears blue or grey, more or less light or dark, according to its quantity, just as the black veins of the blood appear to us blue through the skin. On the contrary, the pigment accumulated in the stroma or between the muscular fibres of the iris exhibits its natural yellow, brown, or almost black colouring, according to the quantity of it, under the form of a trail radiating very clearly from the pupil towards the periphery of the eye occupying one-third, two-thirds, or even the whole of the iris.
Seen at a certain distance, irises without pigment in their stroma appear blue or grey; those having the whole or the greater part of this charged with pigment appear brown, dark brown, or almost black, according to the quantity of this pigment. But irises having a blue or grey foundation strewn with yellowish spots of pigment appear green, yellow, yellowish-grey, greenish-grey, etc.
There are thus distinguishable only three fundamental shades of the iris, or, as is commonly said, of the colour of the eyes: light (blue or grey); dark (bright or dull brown or black); and intermediate shades (green, yellow, yellowish-grey, greenish-grey, etc.). This classification is entirely based on the quantity of pigment in the iris.
It is only in fair European races that blue or grey eyes are found, perhaps also in the Turco-Ugrian races; light-brown eyes are met with among some Mongolians. In all the other populations of the earth the eyes are dark-brown or black. It is the same with the colouring of the hair. It varies appreciably among the wavy-haired races, much less so among the straight and frizzy-haired races, and remains always black among the woolly-haired races. Four principal shades can be distinguished in the hair—black, dark-brown, chestnut-brown (châtain in French), and fair. In this last shade, golden must be separated from flaxen and dull grey-reddish hair. Red hair of all shades is only an individual anomaly, accompanied besides, almost always, by freckles (ephelides) on the face and neck. There are no red-haired races, but light and chestnut hair may have a reddish reflection in it. Red hair is very common in countries where several white-coloured races (brown or fair) are intermixed. In these crossed races there are found heads of hair of all colours—black, brown, fair, reddish-brown, dull-grey, chestnut, etc. This is the natural result of the intermixture of blood. Among a dark-haired people, which has remained free from intermixture, or has only intermingled with dark-haired races, an exceptional red-haired individual constitutes a pathological condition, called “erythrism” by Broca. Erythrism can only manifest itself in certain races; at least, until now no example has been instanced among the Negroes; on the other hand, erythrism is somewhat common among the Jews of Europe, and among such Jews it is most frequently associated with frizzy hair.[53]
The colouring of the hair depends not only on the pigment, but on the more or less quantity of air in the medulla of the hair, which blends the white and grey tones with the general tint given by the pigment. In the air, the hair fades, becomes less highly coloured, duller. Certain acids of the perspiration render the hair reddish-brown, as for instance, under the arm-pit.
At birth pigment is found in the body in less quantity than in the adult state. Every one knows that the hair of children, often light-coloured at birth and in early years, becomes darker as they grow up. Almost all our European children are born with blue eyes, and the pigment only begins to increase in the iris, transforming the eyes into grey, brown, or black at the end of some weeks, or even months after birth. New-born Chinese, Botocudos, Malays, Kalmuks, are much less yellow than the adults of these people, and, lastly, Negroes at birth are of a reddish-chocolate or copper colour, which only becomes darker at the end of three or four days, beginning in certain places, such as the nape, nipples, scrotum, etc.
The presence of temporary spots of pigment noticed among new-born Japanese by Grimm and Baelz, among the Chinese by Matignon, among the Tagals of the Philippines by Collignon, and among the Eskimo by Sören-Hansen,[54] is more puzzling. These are somewhat large blue, grey, or black spots, situated in the sacro-lumbar region and on the buttocks, which disappear about the age of two, three, or five years. The existence of these spots, like that of the ephelides in the European child, would prove rather the migration of pigmental granules to the places selected than a general increase of them. In most races women appear to have clearer skin than men; in that respect, as in many other characters, they have a closer resemblance to children. It is thought by some that the hair of women is lighter than that of men among European races.[55]
Among Negroes the pigment is visible not only on the skin, in the hair, and the iris, but also in the sclerotic, in the mucous membrane of the lips, the mouth, the genital organs, etc.; the internal organs, even, are not free from it; the suprarenal capsules, the mesentery, the liver, the spleen, are often coloured with black spots of pigment, and even the brain contains numerous pigmented points in its envelopes and in its grey matter. Such an abundance of pigment would become a danger to the White, as is proved by certain diseases, melanism, for example, in which the pigment especially invades the viscera, or Addison’s disease, in which, on the contrary, there is an over-production of pigment in the skin and the mucous membranes.