Professor Metchnikoff's volume, on "The Prolongation of Life:
Studies in Optimistic Philosophy," was published in 1907, and is in
some respects the most original of his works. In it he carries much
further the arguments and the studies to which he made brief
allusion in "The Nature of Man," and he lays down certain
principles for the prolongation of life which have been put into
practice by a large number of people during the last two or three
years, and are steadily gaining more attention. Sour milk as an
article of diet appears to have a peculiar value in arresting the
supposed senile changes which are largely due to auto-intoxication
or self-poisoning.
_I.--Senile Debility_
When we study old age in man and the lower animals, we observe certain
features common to both. But often among vertebrates there are found
animals whose bodies withstand the ravages of time much better than that
of man. I think it a fair inference that senility, that precocious
senescence which is one of the greatest sorrows of humanity, is not so
profoundly seated in the constitution of the higher animals as has
generally been supposed. The first facts which we must accept are that
human beings who reach extreme old age may preserve their mental
qualities, notwithstanding serious physical decay, and that certain of
the higher animals can resist the influence of time much longer than is
the case with man under present conditions.
Many theories have been advanced regarding the cause of senility. It is
certain that many parts of the body continue to thrive and grow even in
old age, as, for instance, the nails and hair. But I believe that I have
proved that in many parts of the body, especially the higher elements,
such as nervous and muscular cells, there is a destruction due to the
activity of the white cells of the blood. I have shown also that the
blanching of the hair in old age is due to the activity of these white
cells, which destroy the hair pigment. Progressive muscular debility is
an accompaniment of old age; physical work is seldom given to men over
sixty years of age, as it is notorious that they are less capable of it.
Their muscular movements are feebler, and soon bring on fatigue; their
actions are slow and painful. Even old men whose mental vigour is
unimpaired admit their muscular weakness. The physical correlate of this
condition is an actual atrophy of the muscles, and has for long been
known to observers. I have found that the cause of this atrophy is the
consumption of the muscle fibres by what I call phagocytes, or eating
cells, a certain kind of white blood cells.
In the case of certain diseases we find symptoms, which look like
precocious senility, due to the poison of the disease. It is no mere
analogy to suppose that human senescence is the result of a slow but
chronic poisoning of the organism. Such poisons, if not completely
destroyed or got rid of, weaken the tissues, the functions of which
become altered or enfeebled in which the latter have the advantage. But
we must make further studies before we can answer the question whether
our senescence can be ameliorated.
The duration of the life of animals varies within very wide limits. As a
general rule, small animals do not live so long as large ones, but there
is no absolute relation between size and longevity, since parrots,
ravens, and geese live much longer than many mammals, and than some much
larger birds. Buffon long ago argued that the total duration of life
bore some definite relation to the length of the period of growth, but
further inquiry shows that such a relation cannot be established.
Nevertheless, there is something intrinsic in each kind of animal which
sets a definite limit to the length of years it can attain. The purely
physiological conditions which determine this limit leave room for a
considerable amount of variation in longevity. Duration of life,
therefore, is a character which can be influenced by the environment.
The duration of life in mammals is relatively shorter than in birds, and
in the so-called cold-blooded vertebrates. No indication as to the cause
of this difference can be found elsewhere than in the organs of
digestion. Mammals are the only group of vertebrate animals in which the
large intestine is much developed. This part of the alimentary canal is
not important, for it fulfils no notable digestive function. On the
other hand, it accommodates among the intestinal flora many microbes
which damage health by poisoning the body with their products. Among the
intestinal flora there are many microbes which are inoffensive, but
others are known to have pernicious properties, and auto-intoxication,
or self-poisoning, is the cause of the ill-health which may be traced to
their activity. It is indubitable that the intestinal microbes or their
poisons may reach the system generally, and bring harm to it. I infer
from the facts that the more the digestive tract is charged with
microbes, the more it is a source of harm capable of shortening life. As
the large intestine not only is that part of the digestive tube most
richly charged with microbes, but 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 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. Now the
attempt to destroy the intestinal microbes by the use of chemical agents
has little chance of success, and the intestine itself may be harmed
more than the microbes. If, however, we observe the new-born child we
find that, when suckled by its mother, its intestinal microbes are very
different and much fewer than if it be fed with cows' milk. I am
strongly convinced that it is advantageous to protect ourselves by
cooking all kinds of food which, like cows' milk, are exposed to the
air. It is well-known that other means--as, for instance, the use of
lactic acid--will prevent food outside the body from going bad. Now as
lactic fermentation serves so well to arrest putrefaction in general,
why should it not be used for the same purpose within the digestive
tube? It has been clearly proved that the microbes which produce lactic
acid can, and do, control the growth of other microbes within the body,
and that the lactic microbe is so much at home in the human body that it
is to be found there several weeks after it has been swallowed.
From time immemorial human beings have absorbed quantities of lactic
microbes by consuming in the uncooked condition substances such as
soured milk, kephir, sauerkraut, or salted cucumbers, which have
undergone lactic fermentation. By these means they have unknowingly
lessened the evil consequences of intestinal putrefaction. The fact that
so many races make soured milk and use it copiously is an excellent
testimony to its usefulness, and critical inquiry shows that longevity,
with few traces of senility, is conspicuous amongst peoples who use sour
milk extensively.
A reader who has little knowledge of such matters may be surprised by my
recommendation to absorb large quantities of microbes, as the general
belief is that microbes are all harmful. This belief, however, is
erroneous. There are many useful microbes, amongst which the lactic
bacilli have an honourable place. If it be true that our precocious and
unhappy old age is due to poisoning of the tissues, the greater part of
the poison coming from the large intestine, inhabited by numberless
microbes, it is clear that agents which arrest intestinal putrefaction
must at the same time postpone and ameliorate old age. This theoretical
view is confirmed by the collection of facts regarding races which live
chiefly on soured milk, and amongst which great ages are common.
_IV.--An Ideal Old Age_
As I have shown in the "Nature of Man," the human constitution as it
exists to-day, being the result of a long evolution and containing a
large animal element, cannot furnish the basis of rational morality. The
conception which has come down from antiquity to modern times, of a
harmonious activity of all the organs, is no longer appropriate to
mankind. Organs which are in course of atrophy must not be re-awakened,
and many natural characters which, perhaps, were useful in the case of
animals, must be made to disappear in men.
Human nature which, like the constitutions of other organisms, is
subject to evolution, must be modified according to a definite ideal.
Just as a gardener or stock-raiser is not content with the existing
nature of the plants and animals with which he is occupied, but modifies
them to suit his purposes, so also the scientific philosopher must not
think of existing human nature as immutable, but must try to modify it
for the advantage of mankind. As bread is the chief article in the human
food, attempts to improve cereals have been made for a very long time,
but in order to obtain results much knowledge is necessary. To modify
the nature of plants, it is necessary to understand them well, and it is
necessary to have an ideal to be aimed at. In the case of mankind the
ideal of human nature, towards which we ought to press, may be formed.
In my opinion this ideal is "orthobiosis"--that is to say, the
development of human life, so that it passes through a long period of
old age in active and vigorous health, leading to a final period in
which there shall be present a sense of satiety of life, and a wish for
death.
Just as we must study the nature of plants before trying to realise our
ideal, so also varied and profound knowledge is the first requisite for
the ideal of moral conduct. It is necessary not only to know the
structure and functions of the human organism, but to have exact ideas
on human life as it is in society. Scientific knowledge is so
indispensable for moral conduct that ignorance must be placed among the
most immoral acts. A mother who rears her child in defiance of good
hygiene, from want of knowledge, is acting immorally towards her
offspring, notwithstanding her feeling of sympathy. And this also is
true of a government which remains in ignorance of the laws which
regulate human life and human society.
If the human race come to adopt the principles of orthobiosis, a
considerable change in the qualities of men of different ages will
follow. Old age will be postponed so much that men of from sixty to
seventy years of age will retain their vigour, and will not require to
ask assistance in the fashion now necessary. On the other hand, young
men of twenty-one years of age will no longer be thought mature or ready
to fulfil functions so difficult as taking a share in public affairs.
The view which I set forth in the "Nature of Man" regarding the danger
which comes from the present interference of young men in political
affairs has since then been confirmed in the most striking fashion.
It is easily intelligible that in the new conditions such modern idols
as universal suffrage, public opinion, and the _referendum_, in which
the ignorant masses are called on to decide questions which demand
varied and profound knowledge, will last no longer than the old idols.
The progress of human knowledge will bring about the replacement of such
institutions by others, in which applied morality will be controlled by
the really competent persons. I permit myself to suppose that in these
times scientific training will be much more general than it is just now,
and that it will occupy the place which it deserves in education and in
life.
Our intelligence informs us that man is capable of much, and, therefore,
we hope that he may be able to modify his own nature and transform his
disharmonies into harmonies. It is only human will that can attain this
ideal.