. 98.--Surface of the Palm of the Hand, showing the
Openings of the Sweat Glands and the Grooves between the Papillae of the
Skin. (Magnified 4 diameters.) [In the smaller figure the same epidermal
surface is shown, as seen with the naked eye.]]

Experiment 123. Of course the living skin can be examined only in a
general way. Stretch and pull it, and notice that it is elastic. Note
any liver spots, white scars, moles, warts, etc. Examine the outer skin
carefully with a strong magnifying glass. Study the papillae on the
palms. Scrape off with a sharp knife a few bits of the scarf skin, and
examine them with the microscope.

236. The Hair. Hairs varying in size cover nearly the entire body,
except a few portions, as the upper eyelids, the palms of the hands, and
the soles of the feet.

The length and diameter of the hairs vary in different persons, especially
in the long, soft hairs of the head and beard. The average number of hairs
upon a square inch of the scalp is about 1000, and the number upon the
entire head is estimated as about 120,000.

Healthy hair is quite elastic, and may be stretched from one-fifth to
one-third more than its original length. An ordinary hair from the head
will support a weight of six to seven ounces. The hair may become strongly
electrified by friction, especially when brushed vigorously in cold, dry
weather. Another peculiarity of the hair is that it readily absorbs
moisture.

237. Structure of the Hair. The hair and the nails are structures
connected with the skin, being modified forms of the epidermis. A hair is
formed by a depression, or furrow, the inner walls of which consist of the
infolded outer skin. This depression takes the form of a sac and is called
the hair-follicle, in which the roots of the hair are embedded. At
the bottom of the follicle there is an upward projection of the true skin,
a papilla, which contains blood-vessels and nerves. It is covered
with epidermic cells which multiply rapidly, thus accounting for the rapid
growth of the hair. Around each papilla is a bulbous expansion, the hair
bulb, from which the hair begins to grow.

[Illustration: Fig. 99.--Epidermis of the Foot.

It will be noticed that there are only a few orifices of the sweat glands
in this region. (Magnified 8 diameters.)]

The cells on the papillae are the means by which the hairs grow. As these
are pushed upwards by new ones formed beneath, they are compressed, and
the shape of