This discovery was sufficient to ascertain the point in question:  for it appeared afterwards that the Cuticle, when divided according to this discovery from the other lamina, was semi-transparent; that the cuticle of the blackest negroe was of the same transparency and colour, as that of the purest white; and hence, the true skins of both being invariably the same, that the mucosum corpus was the seat of colour.

This has been farther confirmed by all subsequent anatomical experiments, by which it appears, that, whatever is the colour of this intermediate coagulated substance, nearly the same is the apparent colour of the upper surface of the skin.  Neither can it be otherwise; for the Cuticle, from its transparency, must necessarily transmit the colour of the substance beneath it, in the same manner, though not in the same degree, as the cornea transmits the colour of the iris of the eye.  This transparency is a matter of ocular demonstration in white people.  It is conspicuous in every blush; for no one can imagine, that the cuticle becomes red, as often as this happens:  nor is it less discoverable in the veins, which are so easy to be discerned; for no one can suppose, that the blue streaks, which he constantly sees in the fairest complexions, are painted, as it were, on the surface of the upper skin.  From these, and a variety of other observations[081], no maxim is more true in physiology, than that on the mucosum corpus depends the colour of the human body; or, in other words, that the mucosum corpus being of a different colour in different inhabitants of the globe, and appearing through the cuticle or upper surface of the skin, gives them that various appearance, which strikes us so forcibly in contemplating the human race.

As this can be incontrovertibly ascertained, it is evident, that whatever causes cooperate in producing this different appearance, they produce it by acting upon the mucosum corpus, which, from the almost incredible manner in which the cuticle[082] is perforated, is as accessible as the cuticle itself.  These causes are probably those various qualities of things, which, combined with the influence of the sun, contribute to form what we call climate.  For when any person considers, that the mucous substance, before-mentioned, is found to vary in its colour, as the climates vary from the equator to the poles, his mind must be instantly struck with the hypothesis, and he must adopt it without any hesitation, as the genuine cause of the phaenomenon.