If life had not an irresistible tendency to preserve itself, it would no longer exist today. The instinct of self-preservation makes the herd panic when the prairie catches fire. The wild animal reacts instinctively against adverse conditions in its environment in such a way as to assure the continuity of its existence. In man this reaction is both automatic and voluntary.

The law of self-preservation is written in the structure of our body and expressed in a very special mode of unconscious activity in our tissues; the adaptive function. To some extent the organism models itself on events; it automatically improvises a manner of facing each new situation. This manner is of such a land that it tends to make our continuance as long as possible. Confronted with danger, the physical processes always take the direction which leads to the maximum survival of the individual. Thanks to this power of adaptation in all anatomical systems, the onslaughts of the external world, instead of wearing out our organs, strengthen them. life is preserved and intensified by the struggle against heat, cold, rain, wind and hunger. In the same way, the attacks of bacteria, of other men, of cares and sorrows bring into play conservative mechanisms in our bodies and minds without our being aware of it. They provoke a spontaneous effort in heart, blood vessels, brain, glands and muscles; in fact in all our organs. Warm-blooded animals are so made that the interior environment of the cell tissues must remain invariable. Life can only be preserved on these terms. Since the external environment is essentially variable, the great anatomical systems work full time to neutralize these changes and to maintain the constancy of the internal milieu. The law of adaptation is to the living world what the second law of thermodynamics is to the cosmic. This strange function takes on as many aspects as the various new situations encountered by the tissues and tissue fluids. Not being the specific expression of any organic system, it can be defined only by its purpose. Its means vary: its end remains the same - the conservation of life. The organism fights disease by producing substances which destroy the microbes; against hemorrhages by weakness and sometimes by a momentary stoppage of the heartbeats; against privation of food by diminishing the chemical changes in the tissues; against old age by slowing down the tempo of the physiological rhythm. The spontaneous defense produced by the organism is similar to the resistance opposed by a stable physical system to any factor which tends to modify its equilibrium. If, for example, one dissolves sugar in water, the temperature is lowered and this reduction of heat makes the sugar less soluble. The law of adaptation is as essential to the world of living things as Le Chatelier's principle is to that of physics. It represents the principal mechanism by which life is preserved.

Human beings have become partly conscious of this obstinate attachment to existence. We have an innate fear of death. To us of the West, life appears as the supreme good. Anyone who tries to lay hands on our land, our money or on anything else indispensable to our survival becomes our mortal enemy. To fight an invader has always been considered the noblest of duties. Like the wild animals who devour each other in the jungle, human beings struggle incessantly for self-preservation. The same motive drives the tiger to conquer the prey which prevents it from dying of hunger, and drives civilized man to conquer markets and acquire raw materials. The fight for survival demands incessant activity of body and mind. Life can only be preserved and increased by effort. We recoil from no effort, however painful, when it is a question of surviving. Even when life is a torment, we still try to hold on to it. To keep alive man will consent to be the slave of a machine or to do stultifying work in an office. He will not shrink from the long sufferings of poverty, from dishonorable flight from the enemy, from the infirmities of old age or from the hopeless struggle against incurable disease. The very structure of our body and of our consciousness imposes on us as a primary duty the obligation to maintain life.

This tendency of life to conserve itself seems less irresistible in its conscious aspect than in its unconscious. Intelligence and will do not watch over our existence as unremittingly as does the automatism of the adaptive systems. The great sympathetic nervous system is a more vigilant guardian of the organism than the brain is. Man is the only animal who occasionally prefers death to life. He commits suicide or acquires habits of living which are equivalent to suicide. In all epochs of history man has considered it an honor to die in battle. His behavior is not invariably inspired by the principle of self-preservation.

Man is, as we know, free to violate every natural law. He is guided not by instinct but by intelligence, and intelligence is fallible. By an effort of will, he can control even his deepest impulses. He can silence even the call of life itself. When life ceases to have any value for him, he kills himself. He destroys, in fact, what is already dead.

Stranger still, civilized beings have established customs which render life itself impossible, such as the herding together of people in industrial towns, the suppression of natural modes of existence, excessive drinking and the throwing off of all moral restraint But these errors are mainly due to ignorance of the conditions life exacts, for Western man has a mania to live. This frenzy can be measured by the enormous efforts he makes to avoid dying. Though he does not realize that many modern habits weaken and destroy human beings, he realizes the immense usefulness of hygiene and medicine and has made every effort to develop these sciences. Everywhere, research laboratories have been built at great expense to further our knowledge of chemistry, bacteriology, and physiology; everywhere great medical schools are being set up. New York is dominated by the vast buildings of the Medical Center of Columbia University while on the bank of the East River there looms the huge mass of the Rockefeller Institute.