ut is relatively more capacious in
mammals than in any other vertebrates, it is a just inference that the
duration of life of mammals has been notably shortened as the result of
chronic poisoning from an abundant intestinal flora.

When we come to study the duration of human life, it is impossible to
accept the view that the high mortality between the ages of seventy and
seventy-five indicates a natural limit to human life. The fact that many
men from seventy to seventy-five years old are well preserved, both
physically and intellectually, makes it impossible to regard that age as
the natural limit of human life. Philosophers such as Plato, poets such
as Goethe and Victor Hugo, artists such as Michael Angelo, Titian, and
Franz Hals, produced some of their most important works when they had
passed what some regard as the limit of life. Moreover, deaths of people
at that age are rarely due to senile debility. Centenarians are really
not rare. In France, for instance, nearly 150 centenarians die every
year, and extreme longevity is not limited to the white races. Women
more frequently become centenarians than men--a fact which supports the
general proposition that male mortality is always greater than that of
the other sex.

It has been noticed that most centenarians have been people who were
poor or in humble circumstances, and whose life has been extremely
simple. It may well be said that great riches do not bring a very long
life. Poverty generally brings with it sobriety, especially in old age,
and sobriety is certainly favourable to long life.

_II.--The Study of Natural Death_

It is surprising to find how little science really knows about death. By
natural death I mean to denote death due to the nature of the organism,
and not to disease. We may ask whether natural death really occurs,
since death so frequently comes by accident or by disease; and certainly
the longevity of many plants is amazing. Such ages as three, four, and
five thousand years are attributed to the baobab at Cape Verd, certain
cypresses, and the sequoias of California. It is plain that among the
lower and higher plants there are cases where natural death does not
exist; and, further, so far as I can ascertain, it looks as if poisons
produced by their own bodies were the cause of natural death among the
higher plants where it does occur.

In the human race cases of what may be called natural death are
extremely rare; the death of old people