lor 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.]

_Hairs_ are horny appendages of the skin, and, with the exception of the
hands, the soles of the feet, the backs of the fingers and toes, between
the last joint and the nail, and the upper eyelids, are distributed more
or less abundantly over every part of the surface of the body. Over the
greater part of the surface the hairs are very minute, and in some
places are not actually apparent above the level of the skin; but the
hair of the head, when permitted to reach its full growth, attains a
length of from twenty inches to a yard, and, in rare instances, even six
feet. A hair may be divided into a middle portion, or _shaft_, and two
extremities; a peripheral extremity, called the _point;_ and a central
extremity, inclosed within the hair sac, or follicle, termed the _root_.
The root is somewhat greater in diameter than the shaft, and cylindrical
in form, while its lower part expands into an oval mass, called the
_bulb_. The shaft of the hair is not often perfectly cylindrical, but is
more or less flattened, which circumstance gives rise to waving and