is usually due to infectious
disease, particularly pneumonia, or to apoplexy. The close analogy
between natural death and sleep supports my view that it is due to an
auto-intoxication of the organism, since it is very probable that sleep
is due to "poisoning" by the products of organic activity.

Although the duration of the life of man is one of the longest amongst
mammals, men find it too short. Ought we to listen to the cry of
humanity that life is too short, and that it will be well to prolong it?
If the question were merely one of prolonging the life of old people,
without modifying old age itself, the answer would be doubtful. It must
be understood, however, that the prolongation of life will be associated
with the preservation of intelligence and of the power to work. When we
have reduced or abolished such causes of precocious senility as
intemperance and disease, it will no longer be necessary to give
pensions at the age of sixty or seventy years. The cost of supporting
the old, instead of increasing, will diminish progressively. We must use
all our endeavors to allow men to complete their normal course of life,
and to make it possible for old men to play their parts as advisers and
judges, endowed with their long experience of life.

From time immemorial suggestions have been made for the prolongation of
life. Many elixirs have been sought and supposed to have been found, but
general hygienic measures have been the most successful in prolonging
life and in lessening the ills of old age. That is the teaching of Sir
Herman Weber, himself of very great age, who advises general hygienic
principles, and especially moderation in all respects. He advises us to
avoid alcohol and other stimulants, as well as narcotics and soothing
drugs. Certainly the prolongation of life which has come to pass in
recent centuries must be attributed to the advance of hygiene; and if
hygiene was able to prolong life when little developed, as was the case
until recently, we may well believe that with our greater knowledge a
much better result will be obtained.

_III.--The Use of Lactic Acid_

The general measures of hygiene directed against infectious diseases
play a part in prolonging the lives of old people; but, in addition to
the microbes which invade the body from outside, there is a rich source
of harm in microbes which inhabit the body. The most important of these
belong to the intestinal flora which is abundant and varied. N