the food are retained to promote the growth of the body, those which are
useless or injurious are in various ways expelled. There are, perhaps,
few parts of the body more actively concerned in this removal than the
skin.

[Illustration: Fig. 46: An ideal
view of the papillae. 1, 1. Cutis vera.
2.2. Papillary layer. 3, 3. Arteries of the papillae.
4, 4. Nerves of the papillae. 5, 5. Veins of the papillae.]

The skin is a membranous envelope covering the entire body. It consists
of two layers, termed the Cutis Vera, or true skin, and the Epidermis,
or cuticle. The _Cutis Vera_ is composed of fibers similar to those of
the cellular tissue. It consists of white and yellow fibers, which are
more densely woven near the surface than deeper in the structure; the
white give strength, the yellow strength and elasticity combined. The
true skin may be divided into two layers, differing in their
characteristics, and termed respectively the superficial or papillary
layer, and the deep or fibrous layer. Upon the external surface, are
little conical prominences, known as _papillae_. The papillae are
irregularly distributed over the body, in some parts being smaller and
more numerous than in others, as on the finger-ends, where their summits
are so intimately connected as to form a tolerably smooth surface. It is
owing to their perfect development, that the finger-tips are adapted to
receive the most delicate impressions of touch. Although every part of
the skin is sensitive, yet the papillae are extremely so, for they are
the principal means through which the impressions of objects are
communicated. Each papilla not only contains a minute vein and artery,
but it also incloses a loop of sensitive nerves. When the body is
exposed to cold, these papillae can be more distinctly seen in the form