rially, and become diseased, by the redundant waste matter that
should be carried from the system. If a person is vigorous, the action
of the organs, whose functions are similar to those of the skin, as
channels for the exit of waste matter, will be increased, and thus
relieve the diseased state of the body. But the over-taxing of these
organs, to relieve the system, often produces a diseased action in
themselves.

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What were his conclusions? 655. What is the average amount of
perspiration every twenty-four hours? What is insensible perspiration?
What is sensible perspiration? How can the existence of the excretion
of the skin be shown? Give the 2d experiment. 656. Why is it important
that these excretions be maintained regularly?

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[Illustration: Fig. 117. 1, 1, The lines, or ridges of the cuticle, cut
perpendicularly. 2, 2, 2, 2, 2, The furrows, or wrinkles of the same. 3,
The cuticle. 4, 4, 4, The colored layer of the cuticle. 5, 5, The cutis
vera. 6, 6, 6, 6, 6, The papillae. 7, 7, Small furrows between the
papillae. 8, 8, 8, 8, The deeper furrows between each couple of the
papillae. 9, 9, Cells filled with fat. 10, 10, 10, The adipose layer, with
numerous fat vesicles. 11, 11, 11, Cellular fibres of the adipose tissue.
12, Two hairs. 13, A perspiratory gland, with its spiral duct. 14,
Another perspiratory gland, with a duct less spiral. 15, 15, Oil-glands
with ducts opening into the sheath of the hair, (12.)]

_Note._--Let the pupil review the anatomy and physiology of the skin
from Fig. 117 or from anatomical outline plate No. 9.

CHAPTER XXXIII.

HYGIENE OF THE SKIN.

657. The sensibility of the skin, and the activity of the oil and
perspiratory glands, are modified by the condition of the cuticle, the
temperature of the skin and body, the purity and warmth of the air,
and the character of the light to which the body is exposed. Thus, to
maintain a healthy action of every part of this membrane, attention
should be given to _Clothing_, _Bathing_, _Light_, and _Air_.

658. CLOTHING, in itself, does not bestow heat, but is chiefly useful
in preventing the escape of heat from the body, and in defending it
from the temperature of the atmosphere. In selecting and applying
clothing to our persons, the following suggestions should be
observed.

659. _The material for clothing should be a bad conductor of heat_;
that is, it should have little tende