of the
true skin. While successive layers are formed on the exterior of the
true skin, the external cuticular layers are converted into dry,
flattened scales, by the evaporation of their fluid contents. The
thickness of the cuticle is formed mainly from these scales.

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637-656. _Give the physiology of the skin._ 637. What is said of the
skin? 638. Give a function of the cuticle. Does it vary in thickness
on different parts of the body? Give examples. 630. Mention another
use of the cuticle. 640. What is the cuticle originally?

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641. The cuticle is, therefore, undergoing a constant process of
formation and growth at its under part, to compensate for the wear
that is taking place continually on its surface. A proper thickness of
the cuticle is in this manner preserved; the faculty of sensation and
that of touch are properly regulated; the places of the little scales,
which are continually falling off under the united influence of
friction and ablution, are supplied; and an action necessary, not
merely to the health of the skin, but to that of the entire body, is
established.

642. Whenever the cuticle is exposed to moderate and repeated
friction, it becomes thicker and tougher, as may be seen in the
cuticle of the lady's finger that plies the needle and in the hard or
callous appearance of the hands of farmers masons, and other
mechanics. This enables them to handle the utensils and materials used
in their vocations without pain or inconvenience.

_Observations._ 1st. When the joints of the feet are subjected to
moderate and continued pressure or friction, frequently one or more of
the papillae enlarge. This is accompanied with a thickening of the
layers of the cuticle, which is termed a "callosity," or "corn." These
thickened layers of the cuticle are broad at the top and narrow at the
bottom, and the enlarged mass is conical, with the point innermost.
When pressed upon by a tight shoe, these sensitive papillae cause
pain.

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How is the thickness of the cuticle mainly formed? 641. Describe the
changes of this membrane. Show the necessity of this constant growth.
642. How does moderate and repeated friction affect the cuticle? Give
examples. What is the benefit derived from having the cuticle thus
changed? What is the result if the joints of the feet are subjected to
moderate and continued pressure? What is the form of a "corn"?