scales. As soon as dry, they are removed in the form of scurf, and
replaced by new ones from the cutis vera. These scales may be removed by
a wet-sheet pack, or by friction. The cuticle is constantly undergoing
renewal. This layer serves to cover and protect the nervous tissue of
the true skin beneath. We may here observe that the cuticle contains the
pigment for coloring the skin. In dark races, as the negro, the cuticle
is very thick and filled with black pigment. The radiation of animal
heat is dependent upon the thickness and color of this cuticle. Thus, in
the dark races, the pigment cells are most numerous, and in proportion
as the skin is dark or fair do we find these cells in greater or lesser
abundance. The skin of the Albino is of pearly whiteness, devoid even of
the pink or brown tint which that of the European always possesses. This
peculiarity must be attributed to the absence of pigment cells which,
when present, always present a more or less dark color. The theory that
_climate_ alone is capable of producing all these diversities is simply
absurd. The Esquimaux, who live in Greenland and the arctic regions of
America, are remarkable for the darkness of their complexion. Humboldt
remarks that the American tribes of the tropical regions have no darker
skin than the mountaineers of the temperate zone. Climate may _modify_
the complexion, but it cannot _make_ it.

[Illustration: Fig. 51.
Structure of the human hair. _A_. External surface of the shaft, showing the
transverse striae and jagged boundary, caused by the imbrications of the scaly
cortex. _B_. Longitudinal section of the shaft, showing the fibrous character of
the medullary substance, and the arrangement of the pigmentary matter. _C_.
Transverse sections, showing the distinction between the cortical and medullary
substances, and the central collection of pigmentary matter, sometimes found in
the latter. Magnified 310 diameters.]