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Page 14
In age atrophy is a prominent change. It is seen in the loss of the
teeth, in the whitening and loss of the hair, in the thinning of the
skin so that it more easily wrinkles, in the thinning and weakening of
the muscles so that there is not only diminished force of muscular
contraction, but weakening of the muscles of support. The back curves
from the action of gravity, the strength of the support of the muscles
at the back not counteracting the pull of the weight of the abdominal
viscera in front. The bones become more porous and more brittle.
The effect of atrophy is also seen in the diminution of all functions,
and in loss of weight in individual organs. That the brain shares in
the general atrophy is evident both anatomically and in function.
Mental activity is more sluggish, impressions are received with more
difficulty, their accuracy may be impaired by accompanying changes in
the sense organs, and the concepts formed from the impressions may
differ from the usual. The slowness of mental action and the
diminution in the range of mental activity excited by impressions, and
the slowness of expression, may give a false idea of the value of the
judgment expressed. The expression changes, the face becomes more
impassive because the facial muscles no longer reflect the constant
and ever changing impressions which the youthful sense organs convey
to a youthful and active brain. That the young should ape the old,
should seek to acquire the gravity of demeanor, to restrain the quick
impulse, is not of advantage. Loss of weight of the body as a whole is
not so apparent, there being a tendency to fat formation owing to the
non-use of fat or fat-forming material which is taken into the body.
One of the most evident alterations is a general diminution in the
fluid of the tissues, to which is chiefly due the lack of plumpness,
the wrinkles of age. The facial appearance of age is given to an
infant when, in consequence of a long-continued diarrhoea, the tissues
become drained of fluid. Every market-man knows that an old animal is
not so available for food, the tissues are tougher, more fibrous, not
so easily disintegrated by chewing. This is due to a relative increase
in the connective tissue which binds all parts together and is
represented in the white fibres of meat.
Senile atrophy is complex in its causes and modes of production. The
atrophy affects different organs in different degree and shows great
variation in situation, in degree and in progress. Atrophic changes of
the blood vessels are of great importance, for this affects the
circulation on which the nutrition of all tissues depends. While there
is undoubted progressive wear of all tissues, this becomes most
evident in the case of the blood vessels of the body. It is rare that
arteries which can be regarded as in all respects normal are found in
individuals over forty, and these changes progress rapidly with
advancing age. So striking and constant are these vascular changes
that they seem almost in themselves sufficient to explain the senile
changes, and this has been frequently expressed in the remark that age
is determined not by years, but by the condition of the arteries.
Comparative studies show the falsity of this view, for animals which
are but little or not at all subject to arterial disease show senile
changes of much the same character as those found in man.
There is another condition which must be considered in a study of
causes of age. In the ordinary course of life slight injuries are
constantly being received and more or less perfectly repaired. An
infection which may but slightly affect the ordinary well-being of the
individual may produce a considerable damage. Excess or deficiency or
improper food, occasional or continued use of alcohol and other
poisons may lead to very definite lesions. Repair after injury is
rarely perfect, the repaired tissue is more susceptible to injury, and
with advancing age there is constant diminution in the ease and
perfection of repair. The effect of the sum of all these changes
becomes operative: a vicious circle is established in which injury
becomes progressively easier to acquire and repair constantly less
perfect. There is some adjustment, however, in that the range of
activities is diminished, the environment becomes narrower and the
organism adapts its life to that environment which makes the least
demands upon it.
Whether there is, entirely apart from all conditions affecting
nutrition and the effect of injuries which disturb the usual cell
activities, an actual senescence of the cells of the body is
uncertain. In the presence of the many factors which influence the
obvious diminution of cell activity in the old, it is impossible to
say whether the loss of cell activity is intrinsic or extrinsic. The
life of the plant cell seems to be immortal; it does not grow old.
Trees die owing to accidents or because the tree acquires in the
course of its growth a mass of tissue in which there is little or no
life, and which becomes the prey of parasites. The growing tissue of a
tree is comprised in a thin layer below the bark, and the life of this
may seemingly be indefinitely prolonged by placing it in a situation
in which it escapes the action of accidental injuries and decay, as by
grafting on young trees. Where the nature of the dead wood is such
that it is immune from parasites and decay, as in the case of the
Sequoias, life seems to be indefinitely prolonged. The growing
branches of one of these trees, whose age has been estimated with
seeming accuracy at six thousand years, are just as fresh and the tree
produces its flowers and fruit in the same degree as a youthful
brother of one thousand years. Nor does old age supervene in the
unicellular organisms. An amoeba assimilates, grows and multiplies
just as long as the environment is favorable.
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