shes of the cutis vera. In their course, each little tube forms a
beautiful spiral coil; and, on arriving at its destination, coils upon
itself in such a way as to constitute an oval-shaped, or globular
ball, called the _perspiratory gland_.

633. The opening of the perspiratory tube on the surface of the
cuticle, namely, "the pores," is also deserving of attention. In
consequence of its extremity being a section of a spirally-twisted
tube, the aperture is oblique in direction, and possesses all the
advantages of a valvular opening, preventing the ingress of foreign
injurious substances to the interior of the tube and gland.

634. "To arrive at something like an estimate of the value of the
perspiratory system, in relation to the rest of the organism, I
counted the perspiratory pores on the palm of the hand, and found 3528
in a square inch. Now each of these pores being the aperture of a
little tube about a quarter of an inch long, it follows, that in a
square inch of skin on the palm of the hand there exists a length of
tube equal to 882 inches, or 73 1/2 feet. Surely such an amount of
drainage as seventy-three feet in every square inch of skin--assuming
this to be the average for the whole body--is something wonderful and
the thought naturally intrudes itself, What if this _drainage_ be
obstructed?

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What is said of the retention of the unctuous matter in the oil-tubes?
632. Of what does the perspiratory apparatus consist? 633. What is
peculiar in the opening of the perspiratory tubes on the surface of
the cuticle? 634. How many perspiratory pores did Dr. Wilson count
upon a square inch of skin on the palm of the hand?

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[Illustration: Fig. 116. A perspiratory gland from the palm of the hand,
magnified forty diameters. 1, 1, A twisted tube composing the gland. 2,
2, The two excretory ducts from the gland. These unite to form one spiral
tube, that perforates the cuticle, (3,) and opens obliquely on its
surface at 4. The gland is imbedded in cells filled with fat, which are
seen at 5, 5.]

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What does fig. 116 represent?

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635. "Could we need a stronger argument for enforcing the necessity of
attention to the skin? On the pulps of the fingers, where the ridges
of the sensitive layer of the true skin are somewhat finer than in the
palm of the hand, the number of pores on a square inch a little
exceeded