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_Observations._ 1st. When we wear a shoe that is too short for the
foot, the edge of the nail is brought against the leather. This
interrupts the forward growth of the nail, and it spreads out on the
sides, and becomes unusually thick. It then presses upon the soft
parts, and is said to "grow into the flesh." The prevention is, to
wear shoes of ample size.

2d. Instances are by no means unfrequent in which the power of
production of the nail at the root becomes entirely destroyed, and it
then grows in thickness only. When this affection occurs, it is often
remarkable what a mass the nail presents. Instances are on record,
where the nail is regularly shed; and, whenever the old nail falls
off, a new one is found beneath it, perfectly formed. Sometimes the
growth in length is not entirely checked, although growth in thickness
is induced; the nail then presents a peculiar appearance.

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What causes the edge of the nail "to grow into the flesh" of the toe?
How prevented?

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CHAPTER XXXVI.

THE NERVOUS SYSTEM.

725. In the preceding chapters, we have seen how various and complex
are many of the motions necessary to maintain the life of an animal
whose organization is superior to all others. We have noted the
wonderful mechanism of the muscular system, in producing the varied
movements of the body, the different processes by which the food is
converted into chyle and mixed with the blood, and the circulation of
this fluid to every organ and tissue of the system, that each may
select from it the very principles which it requires for its growth.

726. Lymphatic absorption commences as soon as nutrition is completed,
and conveys the useless, worn-out particles of different tissues back
into the circulating fluid; while the respiratory organs and secretory
glands perform the work of preparing the waste products to be
eliminated from the body. Each of these processes effects a single
object, and is performed in a regular manner.

727. "They must succeed each other in proper order in propelling every
particle to its proper destination, or life would be sacrificed almost
at the moment of its commencement. There is, therefore, a mutual
dependence of all portions of the machinery of organic life upon each
other, and a necessity for some medium of communication from one organ
to another, by which they may convey mutual information of their