Clinical illustrations of these statements will
be given in another place.
The mysterious process which physiologists call metamorphosis of
tissue, or intestitial change, deserves attention in connection with
our subject. It interests both sexes alike. Unless it goes on
normally, neither boys, girls, men, nor women, can have bodies or
brains worth talking about. It is a process, without which not a step
can be taken, or muscle moved, or food digested, or nutriment
assimilated, or any function, physical or mental, performed. By its
aid, growth and development are carried on. Youth, maturity, and old
age result from changes in its character. It is alike the support and
the guide of health convalescence, and disease. It is the means by
which, in the human system, force is developed, and growth and decay
rendered possible. The process, in itself, is one of the simplest. It
is merely the replacing of one microscopic cell by another; and yet
upon this simple process hang the issues of life and death, of thought
and power.
Carpenter, in his physiology, reports the discovery, which we owe to
German investigation, "that the whole structure originates in a single
cell; that this cell gives birth to others, analogous to itself, and
these again to many future generations; and that all the varied
tissues of the animal body are developed from cells.
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