that of the palm; and on the heels, where the ridges are
coarser, the number of pores on the square inch was 2268, and the
length of the tube 567 inches, 47 1/4 feet.

636. "To obtain an estimate of the length of tube of the perspiratory
system of the whole surface of the body, I think that 2800 might be
taken as a fair average of the number of pores in the square inch; and
consequently, 700, the number of inches in length. _Now, the number of
square inches of surface in a man of ordinary height and bulk is 2500;
the number of pores, therefore, 7,000,000; and the number of inches of
perspiratory tube is 1,750,000; that is, 145,833 feet, or 48,611
yards, or nearly TWENTY-EIGHT miles!_"--_Wilson._

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Give other computations in this paragraph. 635. What is said of the
number of these pores on the pulp of the fingers? On the heels? 536.
What is an average number of pores and length of tube of the whole
surface of the body? Give the summary of the number of pores, and
number or inches of perspiratory tube.

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CHAPTER XXXII.

PHYSIOLOGY OF THE SKIN.

637. The skin invests the whole of the external surface of the body,
following all its prominences and curves, and gives protection to all
the organs it encloses, while each of its several parts has a distinct
use.

638. The cuticle is insensible, and serves as a sheath of protection
to the highly sensitive skin (_cutis vera_) situated beneath it. The
latter feels; but the former blunts the impression which occasions
feeling. In some situations, the cuticle is so dense and thick, as
wholly to exclude ordinary impressions. Of this we see an example in
the ends of the fingers, where the hard and dense nail is the cuticle
modified for the purpose referred to. Were the nervous tissue of the
true skin not thus protected, every sensation would be so acute as to
be unpleasant, and contact with external bodies would cause pain.

639. The cuticle, also, prevents disease, by impeding the evaporation
of the fluids of the true skin, and the absorption of the poisonous
vapors, which necessarily attend various employments. It, however,
affords protection to the system only when unbroken, and then, to the
greatest degree, when covered with a proper amount of oily secretion
from the oil-glands.

640. The cuticle is, originally, a transparent fluid, exuded by the
blood-vessels, and distributed as a thin layer on the surface