120,000. The hair possesses great durability, as is evinced by its
endurance of chemical processes, and by its discovery, in the tombs of
mummies more than two thousand years old. The hair is remarkable for its
elasticity and strength. Hair is found to differ materially from horn in
its chemical composition. According to Vauquelin, its constituents are
animal matter, a greenish-black oil, a white, concrete oil, phosphate of
lime, a trace of carbonate of lime, oxide of manganese, iron, sulphur,
and silex. Red hair contains a reddish oil, a large proportion of
sulphur, and a small quantity of iron. White hair contains a white oil,
and phosphate of magnesia. It has been supposed that hair grows after
death, but this theory was probably due to the lengthening of the hair
by the absorption of moisture from the body or atmosphere.

The _nails_ constitute another class of appendages of the skin. They
consist of thin plates of horny tissue, having a root, a body, and a
free extremity. The root, as well as the lateral portion, is implanted
in the skin, and has a thin margin which is received into a groove of
the true skin. The under surface is furrowed, while the upper is
comparatively smooth. The nails grow in the same manner as the cuticle.

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CHAPTER X.

PHYSIOLOGICAL ANATOMY.

SECRETION.