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