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Chapter VI

ADAPTIVE FUNCTIONS

THERE is a striking contrast between the durability of our body and the transitory character of its elements. Man is composed of a soft, alterable matter, susceptible of disintegrating in a few hours. However, he lasts longer than if made of steel. Not only does he last, but he ceaselessly overcomes the difficulties and dangers of the outside world. He accommodates himself, much better than the other animals do, to the changing conditions of his environment. He persists in living, despite physical, economic, and social upheavals. Such endurance is due to a very particular mode of activity of his tissues and humors. The body seems to mold itself on events. Instead of wearing out, it changes. Our organs always improvise means of meeting every new situation. And these means are such that they tend to give us a maximum duration. The physiological processes, which are the substratum of inner time, always incline in the direction leading to the longest survival of the individual. This strange function, this watchful automatism, makes possible human existence with its specific characters. It is called adaptation.

   All physiological activities are endowed with the property of being adaptive. Adaptation, therefore, assumes innumerable forms. However, its aspects may be grouped into two categories, intraorganic and extraorganic. Intraorganic adaptation is responsible for the constancy of the organic medium and of the relations of tissues and humors. It determines the correlation of the organs. It brings about the automatic repair of tissues and the cure of diseases. Extraorganic adaptation adjusts the individual to the physical, psychological, and economic world. It allows him to survive in spite of the unfavorable conditions of his environment. Under these two aspects, the adaptive functions are at work during each instant of our whole life. They are the indispensable basis of our duration.

   Whatever our sufferings, our joys, and the agitation of the world may be, our organs do not modify their inward rhythm to any great extent. The chemical exchanges of the cells and the humors continue imperturbably. The blood pulsates in the arteries and flows at an almost constant speed in the innumerable capillaries of the tissues. There is an impressive difference between the regularity of the phenomena taking place within our body and the extreme variability of our environment. Our organic states are very steady. But this stability is not equivalent to a condition of rest, or equilibrium. It is due, on the contrary, to the unceasing activity of the entire organism. To maintain the constancy of the blood's composition and the regularity of its circulation, an immense number of physiological processes are required. The tranquillity of the tissues is assured by the converging efforts of all the functional systems. And the more irregular and violent our life, the greater are these efforts. For the brutality of our relations with the cosmic world must never trouble the peace of the cells and humors of our inner world.

   The blood is not subjected to large variations of pressure and volume. However, it receives and loses a great deal of water in an irregular manner. After each meal, it takes in the fluids absorbed by the intestinal mucosa from the food and the digestive juices. At other moments its volume tends to decrease. In the course of digestion, it loses several liters of water, which are used by the stomach, intestines, liver, and pancreas for manufacturing their secretions. An analogous phenomenon occurs during violent muscular exercise, a boxing-match for example, if the perspiration glands work actively. Blood also diminishes in volume in the course of certain diseases, such as dysentery or cholera, when a great deal of liquid passes from the capillary vessels into the lumen of the intestine. The administration of a purgative is followed by a similar waste of water. The gains and losses are exactly counterbalanced by mechanisms regulating the blood volume.

   These mechanisms extend over the whole body. They maintain constant both the pressure and the volume of the blood. The pressure does not depend on the absolute amount of the blood, but on the relation of this amount to the capacity of the circulatory apparatus. This apparatus, however, is not comparable to a system of pipes fed by a pump. It has no analogy with the machines constructed by man. Arteries and veins automatically modify their caliber. They contract or dilate under the influence of the nerves of their muscular envelope. In addition, the walls of the capillaries are permeable. The water of the blood is thus free to enter or to leave the circulatory apparatus. It also escapes from the body through the kidneys, the pores of the skin, the intestinal mucosa, and evaporates in the lungs. The heart realizes the miracle of maintaining constant the pressure of the blood in a system of vessels whose capacity and permeability ceaselessly vary. When blood tends to accumulate in too large a quantity in the right heart, a reflex, starting from the right auricle, increases the rate of cardiac pulsations, and blood escapes more rapidly from the heart into the vessels. Moreover, serum traverses the wall of the capillaries and inundates connective tissue and muscles. In this manner, the circulatory system automatically ejects all excess of fluid. If, on the contrary, the volume and the pressure of the blood diminish, the change is recorded by nerve endings hidden in the wall of the sinus of the carotid artery. This reflex determines a contraction of the vessels and a reduction in the capacity of the circulatory apparatus. At the same time, the fluids of the tissues and those contained in the stomach pass into the vascular system by filtering through the wall of the capillaries. Such are the mechanisms responsible for the nearly perfect constancy of the amount and the tension of the blood.

   The composition of the blood is also very stable. Under normal conditions, the quantity of red cells, plasma, salts, proteins, fats, and sugars varies only in a small measure. It always remains higher than is really necessary for the usual requirements of the tissues. Consequently, unforeseen events, such as privation of food, hemorrhages, or intense and prolonged muscular efforts do not modify in a dangerous manner the state of the organic fluids. The tissues contain abundant reserves of water, salts, fats, proteins, and sugar. Oxygen, however, is not stored anywhere. It must be unceasingly supplied to the blood by the lungs. The organism needs variable quantities of this gas, according to the activity of its chemical exchanges. At the same time it produces more or less carbon dioxide. However, the tension of these gases in the blood remains constant. This phenomenon is due to a mechanism both physicochemical and physiological. A physicochemical equilibrium determines the amount of oxygen taken up by the red corpuscles during their passage through the lungs, and carried by those corpuscles to the tissues. During its journey through the peripheral capillary vessels, the blood absorbs the carbon dioxide set free by the tissues. This acid decreases the affinity of hemoglobin for oxygen. It promotes the passing of the gas from the red corpuscles to the cells of the organs. The exchange of oxygen and carbon dioxide between tissues and blood is due exclusively to the chemical properties of the hemoglobin, the proteins, and the salts of blood plasma.

   A physiological process is responsible for the quantity of oxygen carried by the blood to the tissues. The activity of the respiratory muscles, which give a more or less rapid motion to the thorax and control the penetration of air into the lungs, depends on nervous cells situated in the upper part of the spinal cord. The activity of this center is regulated by the tension of carbon dioxide in the blood. And also by the temperature of the body and by the excess or insufficiency of oxygen in the circulation. A similar mechanism, both physicochemical and physiological, regulates the ionic alkalinity of blood plasma. The intraorganic medium never becomes acid. This fact is all the more surprising as tissues unceasingly produce large quantities of carbonic, lactic, sulphuric acids, etc., which are set free into the lymph. These acids do not modify the reaction of blood plasma, because they are neutralized, or rather buffered, by the presence of bicarbonates and phosphates. Although blood plasma can accept a large quantity of acids without increasing its actual acidity, it must, nevertheless, get rid of them. Carbon dioxide escapes from the body by the lungs. Non-volatile acids are eliminated through the kidneys. The discharge of carbon dioxide by the pulmonary mucosa is a mere physicochemical phenomenon, while the secretion of urine and the motion of the thorax and the lungs require the intervention of physiological processes. The physico-chemical equilibria, which assure the constancy of the organic medium, ultimately depend on the automatic intervention of the nervous system.

   The organs are correlated by the organic fluids and the nervous system. Each element of the body adjusts itself to the others, and the others to it. This mode of adaptation is essentially teleological. If we attribute to tissues an intelligence of the same kind of ours, as mechanists and vitalises do, the physiological processes appear to associate together in view of the end to be attained. The existence of finality within the organism is undeniable. Each part seems to know the present and future needs of the whole, and acts accordingly. The significance of time and space is not the same for our tissues as for our mind. The body perceives the remote as well as the near, the future as well as the present. When pregnancy is nearly completed, the tissues of the vulva and vagina are invaded by fluids. They become soft and extensible. Such a change in their consistency renders the passage of the fetus possible a few days later. At the same time, the mammary glands multiply their cells. Before confinement, they begin to function. They are ready and waiting to feed the child. All these processes are obviously a preparation for a future event.

   When one half of the thyroid gland is removed, the remaining half increases in volume. Generally, it even increases more than is necessary. The organism, as Meltzer has shown, is abundantly provided with factors of safety. In the same way, the extirpation of a kidney is followed by the enlargement of the other one, although the secretion of urine is amply assured by a single normal kidney. If at any time the organism calls upon the thyroid or the kidney for an exceptional effort, these organs will be capable of satisfying the unforeseen demand.

   During the entire history of the embryo the tissues seem to prepare for the future. Organic correlations take place as easily between different periods of time as between different regions of space. These facts are a primary datum of observation. But they cannot be interpreted with the help of our naive mechanistic and vitalistic concepts. The teleological correlation of organic processes is evident in the regeneration of blood after a hemorrhage. First, all the vessels contract. The relative volume of the remaining blood automatically increases. Thus, arterial pressure is sufficiently restored for blood circulation to continue. The fluids of the tissues and the muscles pass through the wall of the capillary vessels and invade the circulatory system. The patient feels intense thirst. The blood immediately absorbs the fluids that enter the stomach and reestablishes its normal volume. The reserves of red cells escape from the organs where they were stored. Finally, the bone marrow begins manufacturing red corpuscles, which will complete the regeneration of the blood. In sum, all parts of the body contribute a concatenation of physiological, physicochemical, and structural phenomena. These phenomena constitute the adaption of the whole to hemorrhage.

   The component parts of an organ, of the eye, for example, appear to associate for a definite, although future, purpose. The skin covering the young retina becomes transparent, as already mentioned, and metamorphoses into cornea and lens. This transformation is considered as due to substances set free by the cerebral part of the eye, the optic vesicle. But the solution of the problem is not given by this explanation. How does it happen that the optic vesicle secretes a substance endowed with the property of rendering the skin translucid? By what means does the future retina induce the skin to manufacture a lens capable of projecting upon its nerve endings the image of the outer world? In front of the lens, the iris shapes itself into a diaphragm. This diaphragm dilates or contracts according to the intensity of the light. At the same time, the sensitivity of the retina increases or decreases. In addition, the form of the lens automatically adjusts itself to near or distant vision. These correlations are obvious facts. But, as yet, they cannot be explained. Possibly they are not what they seem to be. The phenomena may be fundamentally simple. We may miss their oneness. In fact, we divide a whole into parts. And we are astonished that the parts, thus separated, exactly fit each other when they are put together again by our mind. We probably give to things an artificial individuality. Perhaps the frontiers of the organs and of the body are not where we believe them to be located. Neither do we understand the correlations between different individuals, for example, the corresponding existence of the penis and the vagina. Nor the cooperation of two individuals in the same physiological process, such as the fecundation of the egg by the spermatozoon. Those phenomena are not intelligible by the light of our present concepts of individuality, organization, space, and time.

   When skin, muscles, blood vessels, or bones are injured by a blow, a flame, or a projectile, the organism immediately adapts itself to such a new situation. Everything happens as if a series of measures, some immediate, some delayed, were taken by the body in order to repair the lesions of the tissues. As in blood regeneration, heterogeneous and converging mechanisms come into play. They all turn toward the end to be attained, the reconstruction of the destroyed structures. An artery is cut. Blood gushes in abundance. Arterial pressure is lowered. The patient has a syncope. The hemorrhage decreases. A clot forms in the wound. Fibrin occludes the opening of the vessel. Then the hemorrhage definitely stops. During the following days, leucocytes and tissues cells invade the clot of fibrin and progressively regenerate the wall of the artery. Likewise, the organism may heal a small wound of the intestines by its own means. The wounded loop first becomes immobile. It is temporarily paralyzed, and fecal matter is thus prevented from running into the abdomen. At the same time, some other intestinal loop, or the surface of the omentum, approaches the wound and, owing to a known property of peritoneum, adheres to it. Within four or five hours the opening is occluded. Even if the surgeon's needle has drawn the edges of the wound together, healing is due to spontaneous adhesion of the peritoneal surfaces.

   When a limb is broken by a blow, the sharp ends of the fractured bones tear muscles and blood vessels. They are soon surrounded by a bloody clot of fibrin, and by osseous and muscular debris. Then, circulation becomes more active. The limb swells. The nutritive substances necessary for the regeneration of the tissues are brought into the wounded area by the blood. At the seat of the fracture and around it, all structural and functional processes are directed toward repair. Tissues become what they have to be in order to accomplish the common task. For example, a shred of muscle close to the focus of fracture metamorphoses into cartilage. Cartilage, as is well known, is the forerunner of bone in the soft mass temporarily uniting the broken ends. Later, cartilage transforms into osseous tissue. The skeleton is thus regenerated by a substance of exactly the same nature as its own. During the few weeks necessary for the completion of repair, an immense number of chemical, nervous, circulatory, and structural phenomena take place. They are all concatenated. The blood flowing from the vessels at the time of the accident, and the juices from the bone marrow and lacerated muscles, set in motion the physiological processes of regeneration. Each phenomenon results from the preceding one. To the physico-chemical conditions and to the chemical composition of the fluids set free in the tissues must be attributed the actualization within the cells of certain potential properties. And these potential properties give to anatomical structures the power to regenerate. Each tissue is capable of responding, at any moment of the unpredictable future, to all physicochemical or chemical changes of the intraorganic medium in a manner consistent with the interests of the whole body.

   The adaptive aspect of cicatrization is evident in superficial wounds. These wounds are exactly measurable. Their rate of healing can be calculated by Lecomte du Noüy's formulas. And the process of cicatrization thus analyzed. First, we observe that a wound only cicatrizes if cicatrization is advantageous to the body. When the tissues uncovered by the extirpation of the skin are completely protected against microbes, air, and other causes of irritation, regeneration does not take place. In fact, under such conditions it is useless. The wound, therefore, does not heal and remains in its initial state. Such a state is maintained as long as the tissues are guarded against the attacks of the outer world as perfectly as they would be by the regenerated skin. As soon as some blood, a few microbes, or an ordinary dressing is allowed to come in contact with the damaged surface and to irritate it, the process of healing starts and continues irresistibly until cicatrization is complete.

   Skin, as we know, consists of superposed sheets of flat cells, the epithelial cells. These cells lie on the dermis--that is, on a soft and elastic layer of connective tissue containing many small blood vessels. When a piece of skin is removed, the bottom of the wound is seen to consist of fatty tissue and muscles. After three or four days its surface becomes smooth, glistening, and red. Then it abruptly begins to decrease with great rapidity. This phenomenon is due to a sort of contraction of the new tissue covering the wound. At the same time, the skin cells commence to glide over the red surface as a white edge. Finally, they cover its entire area. A definitive scar is formed. This scar is due to the collaboration of two types of tissue, the connective tissue filling the wound, and the epithelial cells, which advance over its surface from the borders. Connective tissue is responsible for the contraction of the wound. Epithelial tissue, for the membrane that ultimately covers it. The progressive decrease of the wounded area in the course of repair is expressed by an exponential curve. However, if one prevents either the epithelial tissue or the connective tissue from accomplishing its respective tasks, the curve does not change. It does not change because the deficiency of one of the factors of repair is compensated by the acceleration of the other. Obviously, the progress of the phenomenon depends on the end to be attained. If one of the regenerating mechanisms fails, it is replaced by the other. The result alone is invariable. And not the procedure. In a like manner, after a hemorrhage, arterial pressure and blood volume are reestablished by two converging mechanisms. On one side, by contraction of the blood vessels and by diminution of their capacity. On the other side, by the bringing of a quantity of liquid from the tissues and the digestive apparatus. But each of these mechanisms is capable of compensating the failure of the other.

   The knowledge of the processes of healing has brought modern surgery into being. Surgeons would not be able to treat wounds if adaptation did not exist. They have no influence on the healing mechanisms. They content themselves with guiding the spontaneous activity of those mechanisms. For example, they manage to bring the edges of a wound, or the ends of a broken bone, into such a position that regeneration takes place without defective scar and deformity. In order to open a deep abscess, treat an infected fracture, perform a Cesarean operation, extirpate a uterus, a portion of the stomach or of the intestines, or raise the roof of the skull and remove a tumor from the brain, they have to make long incisions and extensive wounds. The most accurate sutures would not suffice definitely to close such openings if the organism were not capable of making its own repairs. Surgery is based on the existence of this phenomenon. It has learned to turn adaptation to account. Owing to the extreme ingenious-ness and audacity of its methods, it has surpassed the most ambitious hopes of medicine of former times. Its attainments are the purest triumph of biology. He who has completely mastered its techniques, who understands its spirit, who has acquired the knowledge of human beings and the science of their diseases, truly becomes like God. He possesses the power to open the body, explore the organs, and repair their lesions, almost without risk to the patient. To many people he restores strength, health, and the joy of living. Even to those tortured by incurable diseases, he is always capable of bringing some relief. Men of such type are rare. But their number could easily be increased by a better technical, moral, and scientific education.

   The reason behind such success is simple. Surgery has merely learned that the normal processes of healing must not be hindered. It has succeeded in preventing microbes from getting into wounds. Operations, before the discoveries of Pasteur and Lister, were always followed by invasion of bacteria. Such attacks caused suppuration, gaseous gangrene, and infection of the whole body. They often ended in death. Modern techniques have practically eliminated microbes from operative wounds. In this manner they save the life of the patient and lead him to a rapid recovery. For microbes have the power to obstruct or delay adaptive processes and repair. As soon as wounds were protected against bacteria surgery began to grow. Its methods rapidly developed in the hands of Oilier, Billroth, Kocher, and their contemporaries. In a quarter of a century of stupendous progress they blossomed into the mighty art of Halsted, Tuffier, Harvey Cushing, the Mayos, and of all the great modem surgeons.

   This success came from the clear understanding of certain adaptive phenomena. It is indispensable, not only to preserve the wounds from infection, but also to respect, in the course of operative handling, their structural and functional conditions. Tissues are endangered by most antiseptic substances. They must not be crushed by forceps, compressed by apparatuses, or pulled about by the fingers of a brutal operator. Halsted and the surgeons of his school have shown how delicately wounds must be treated if they are to keep intact their regenerative power. The result of an operation depends both on the state of the tissues and on that of the patient. Modern techniques take into consideration every factor capable of modifying physiological and mental activities. The patient is protected against the dangers of fear, cold, and anesthesia, as well as against infection, nervous shock, and hemorrhages. And if, through some mistake, infection sets in, it can be effectively dealt with. Some day, perhaps, when the nature of healing processes is better known, it will become possible to increase their rapidity. The rate of repair, as we know, varies according to definite qualities of the humors, and especially to their youthfulness. If such qualities could temporarily be given to the blood and the tissues of the patient, recovery from surgical operations would be made much easier. Certain chemical substances are known to accelerate cell multiplication. Possibly, they will be utilized for this purpose. Each step forward in the knowledge of the mechanisms of regeneration will bring about a corresponding progress in surgery. But in the best hospital, as in the desert or the primitive forest, the healing of wounds depends, above all, on the efficiency of the adaptive functions.

   All organic functions are modified, as soon as microbes or viruses cross the frontiers of the body and invade the tissues. Illness sets in. Its characteristics depend on the mode of adjustment of the tissues to the pathological changes of their medium. For instance, fever is the reply of the body to the presence of bacteria and viruses. Other adaptive reactions are determined by the production of poisons by the organism itself, the lack of certain substances indispensable to nutrition, and the disturbances in the activities of various glands. The symptoms of Bright's disease, of scurvy, of exophthalmic goiter, express the accommodation of the organism to substances which diseased kidneys are no longer able to eliminate, to the absence of a vitamine, to the secretion of toxic products by the thyroid gland. The accommodation to pathogenic agents assumes two different aspects. On one side, it opposes their invasion of the body and tends to bring about their destruction. On the other, it repairs the lesions the organism has suffered, and causes the poisons generated by the bacteria or by the tissues themselves to disappear. Disease is nothing but the development of these processes. It is equivalent to the struggle of the body against a disturbing agent and to its effort to persist in time. But it may be, as in cancer or insanity, the expression of the passive decay of an organ, or of consciousness.

   Microbes and viruses are to be found everywhere, in the air, in water, in our food. They are always present at the surface of the skin, and of the digestive and respiratory mucosas. Nevertheless, in many people they remain inoffensive. Among human beings, some are subject to diseases, and others are immune. Such a state of resistance is due to the individual constitution of the tissues and the humors, which oppose the penetration of pathogenic agents or destroy them when they have invaded our body. This is natural immunity. This form of immunity may preserve certain individuals from almost any disease. It is one of the most precious qualities for which man could wish. We are still ignorant of its nature. It appears to depend on some properties of ancestral origin, as well as on others acquired in the course of development. Certain families are observed to be susceptible to tuberculosis, appendicitis, cancer, or mental disorders. Others resist all diseases except the degenerative ones occurring during old age. But natural immunity does not exclusively derive from our ancestral constitution. It may come also from the mode of life and alimentation, as Reid Hunt showed long ago. Some diets were found to increase the susceptibility of mice to experimental typhoid fever. The frequency of pneumonia may also be modified by food. The mice belonging to one of the strains kept in the mousery of the Rockefeller Institute died of pneumonia in the proportion of fifty-two per cent while subjected to the standard diet. Several groups of these animals were given different diets. The mortality from pneumonia fell to thirty-two per cent, fourteen per cent, and even zero, according to the food. We should ascertain whether natural resistance to infections could be conferred on man by definite conditions of life. Injections of specific vaccine or serum for each disease, repeated medical examinations of the whole population, construction of gigantic hospitals, are expensive and not very effective means of preventing diseases and of developing a nation's health. Good health should be natural. Such innate resistance gives the individual a strength, a boldness, which he does not possess when his survival depends on physicians.

   In addition to an inherent resistance to maladies, there is also an acquired resistance. The latter may be spontaneous or artificial. The organism is known to adapt itself to bacteria and viruses by the production of substances capable of directly or indirectly destroying the invaders. Thus, diphtheria, typhoid fever, smallpox, measles, etc., render their victims immune to a second attack of the disease, at least for some time. This spontaneous immunity expresses the adaptation of the organism to a new situation. If a fowl is injected with the serum of a rabbit, the serum of the fowl acquires, after a few days, the property of bringing about an abundant precipitate in the serum of the rabbit. In this way the fowl has been rendered immune to the albumins of the rabbit. Likewise, when bacterial toxins are injected into an animal, this animal produces antitoxins. The phenomenon becomes more complex if the bacteria themselves are injected. These bacteria compel the animal to manufacture substances by which they are agglutinated and destroyed. At the same time, the leucocytes of blood and tissues acquire the power of devouring them, as was discovered by Metchnikoff. Independent phenomena, whose effects are converging, take place under the influence of the pathogenic agent and bring about the destruction of the invading microbes. These processes are endowed with the same characteristics of simplicity, complexity, and finality as other physiological processes.

   The adaptive responses of the organism are due to definite chemical substances. Certain polysaccharids, present in the bodies of bacteria, determine specific reactions of the cells and the humors when they are united with a protein. Instead of the polysaccharids of the bacteria, the tissues of our body manufacture some carbohydrates and lipoids, which possess similar properties. These substances give to the organism the power to attack foreign proteins or foreign cells. In the same way as the microbes, the cells of an animal determine in the organism of another animal the appearance of antibodies. And those cells are finally destroyed by their antibodies. For this reason, the transplantation into a man of a chimpanzee's testicles is not successful. The existence of these adaptive reactions has led to vaccination and to the use of therapeutic serums. Ultimately, to artificial immunity. A great quantity of antibodies develops in the blood of an animal injected with dead or attenuated microbes, viruses, or bacterial poisons. The serum of the animal rendered immune to a disease may sometimes cure patients suffering from the disease in question. It supplies their blood with the antitoxic antibacterial substances which are lacking. Thus, it gives them the power, which most individuals do not possess, to overcome the infection.

   Either alone or with the aid of specific serums and of nonspecific chemical and physical medications, the patient fights against the invading microbes. Meanwhile, lymph and blood are modified by poisons set free by the bacteria and by the waste products of the diseased organism. Profound alterations take place in the whole body. Fever, delirium, and acceleration of the chemical exchanges occur. In dangerous infections, in typhoid fever, pneumonia, and septicemias, for instance, lesions develop in various organs, such as heart, lungs, and liver. The cells then actualize certain properties which, in ordinary life, remain potential. They tend to render the humors deleterious to bacteria, and to stimulate all organic activities. The leucocytes multiply, secrete new substances, undergo precisely such metamorphoses as are needed by the tissues, adapt themselves to the unforeseen conditions created by the pathogenic factors, the defection of organs, the virulence of bacteria, and their local accumulation. They form abscesses in the infected regions, and the ferments contained in the pus of the abscesses digest the microbes. These ferments also possess the power of dissolving living tissues. They thus open a way for the abscess, either toward the skin or some hollow organ. In this manner, pus is eliminated from the body. The symptoms of bacterial diseases express the effort made by tissues and humors to adapt themselves to the new conditions, to resist them, and to return to a normal state.

   In degenerative diseases, such as arteriosclerosis, myocarditis, nephritis, diabetes, and cancer, and those due to alimentary deficiencies, the adaptive functions likewise enter into play. The physiological processes become modified in the manner best suited to the survival of the organism. If the secretion of a gland is insufficient, some other glands augment their activity and volume in order to supplement its work. When the valve protecting the orifice of communication of the left auricle and ventricle allows the blood to flow back, the heart increases in size and strength. Thus, it succeeds in pumping into the aorta an almost normal quantity of blood. This adaptive phenomenon enables the patient to continue to lead a normal existence for several years. When the kidneys are impaired, the arterial pressure rises in order that a larger volume of blood may pass through the defective filter. During the first stage of diabetes, the organism endeavors to compensate the decrease in the quantity of insulin secreted by the pancreas. These diseases generally represent an attempt made by the body to adapt itself to a defective function.

   There are pathogenic agents against which the tissues do not react, which do not elicit any response from the adaptive mechanisms. Such is, for instance, Treponema pallidum, the agent of syphilis. Once Treponema has penetrated the body, it never spontaneously leaves its victim. It takes up its abode in the skin, the blood vessels, the brain, or the bones. Neither the cells nor the humors are able to destroy it. Syphilis yields only to prolonged treatment. Likewise, cancer meets with no opposition from the organism. Tumors, whether benign or malignant, are so much like normal tissues that the body is not aware of their presence. They often develop in individuals who for a long time show no evidence of being affected. The symptoms, when they appear, are not the expression of a reaction of the organism. They are the direct result of the misdoings of the tumor, of its toxic products, of the destruction of an essential organ, or of the compression of a nerve. The progress of cancer is inexorable, because tissues and humors do not react against the invasion of the diseased cells.

   In the course of an illness, the body meets with situations never previously encountered. It tends, nevertheless, to adapt itself to these new conditions by eliminating the pathogenic agents and repairing the lesions they have caused. In the absence of such adaptive power, living beings could not endure, because they are ceaselessly exposed to the attacks of viruses or bacteria, and to the structural failure of innumerable elements of the organic systems. An individual's survival was formerly wholly due to his adaptive capacity. Modern civilization, with the help of hygiene, comfort, good food, soft living, hospitals, physicians, and nurses, has kept alive many human beings of poor quality. These weaklings and their descendants contribute, in a large measure, to the enfeeblement of the white races. We should perhaps renounce this artificial form of health and exclusively pursue natural health, which results from the excellence of the adaptive functions and from the inherent resistance to disease.

   Extraorganic adaption consists in the adjustment of the inner state of the body to the variations of the environment. This adjustment is brought about by the mechanisms responsible for stabilizing physiological and mental activities, and for giving the body its unity. To each change of the surroundings the adaptive functions furnish an appropriate reply, Man can, therefore, stand the modifications of the outside world. The atmosphere is always either wanner or colder than the skin. Nevertheless, the temperature of the humors bathing the tissues, and of the blood circulating in the vessels, remains unchanged. Such a phenomenon depends on the continuous work of the entire organism. Our temperature has a tendency to rise with that of the atmosphere, or when our chemical exchanges become more active, as, for instance, in fever. Pulmonary circulation and respiratory movements then accelerate. A larger quantity of water is evaporated from the pulmonary alveoli. Consequently, the temperature of the blood in the lungs is lowered. At the same time, the subcutaneous vessels dilate and the skin becomes red. The blood rushes to the surface of the body and cools by contact with atmospheric air. If the air is too warm, the skin becomes covered by thin streams of perspiration produced by the sweat glands. This perspiration, in evaporating, brings about a fall in the temperature. The central nervous system and the sympathetic nerves come into play. They increase the rapidity of cardiac pulsations, dilate blood vessels, bring on the sensation of thirst, etc. On the contrary, when the outer temperature falls, the vessels of the skin contract, and the skin itself becomes white. The blood circulates sluggishly in the capillaries. It takes refuge in the inner organs, whose circulation and chemical exchanges are accelerated. Thus, we fight external cold, as we fight heat, by nervous, circulatory, and nutritive changes of our whole body. All the organs, as well as the skin, are maintained in constant activity by exposure to heat, cold, wind, sun, and rain. When we spend our life sheltered from the inclemencies of the weather, the processes regulating the temperature of the blood, its volume, its alkalinity, etc., are rendered useless.

   We become adapted to excitations emanating from the outer world, even when their violence or their weakness modifies, in an exaggerated or insufficient manner, the nerve endings of the sense organs. Excessive light is dangerous. In primitive surroundings men instinctively hide from it. There is a large number of mechanisms capable of protecting the organism from sun rays. The eye is defended by the eyelids and the diaphragm of the iris against any increase in light intensity. Simultaneously, the retina becomes less sensible. The skin opposes the penetration of solar radiations by manufacturing pigment. When these natural defenses are insufficient, lesions of the retina or of the skin occur, and also certain disorders of the viscera and the nervous system. It is possible that lessened reactivity of the nervous system and of the intelligence may eventually result from too strong a light. We must not forget that the most highly civilized races--the Scandinavians, for example--are white, and have lived for many generations in a country where the atmospheric luminosity is weak during a great part of the year. In France, the populations of the north are far superior to those of the Mediterranean shores. The lower races generally inhabit countries where light is violent and temperature equal and warm. It seems that the adaptation of white men to light and to heat takes place at the expense of their nervous and mental development.

   In addition to light rays, the nervous system receives from the cosmic world various excitations. These stimuli are sometimes strong, sometimes weak. Man may be compared to a photographic plate, which must record different intensities of light in the same way. The effect of light on the plate is regulated by a diaphragm and a proper duration of exposure. The organism uses another method. Its adaptation to the unequal intensity of the excitations is obtained by an increase or a decrease of its receptivity. It is well known that the retina becomes much less sensitive when exposed to intense light. Likewise, the mucosa of the nose, after a short time, no longer perceives a bad odor. An intense noise, if produced continuously or at a uniform rhythm, causes little inconvenience. The roaring of the ocean as it pounds the rocks, or the rumbling of a train, does not disturb our sleep. We chiefly notice variations in the intensity of the excitations. Weber thought that, when stimulus increases in geometrical progression, sensation increases only in arithmetical progression. The intensity of sensation augments, therefore, much more slowly than that of excitation. Since we are affected, not by the absolute intensity of a stimulus, but by the difference in intensity of two successive excitations, such mechanism effectively protects our nervous system. Weber's law, although not exact, approximately expresses what takes place. However, the adaptive mechanisms of our nervous systems are not as developed as those of the other organic apparatuses. Civilization has created new stimuli against which we have no defense. Our organism tries in vain to adapt itself to the noises of the large cities and factories, to the agitation of modern life, the worries and the crowding of our days. We do not get used to lack of sleep. We are incapable of resisting hypnotic poisons, such as opium or cocaine. Strange to say, we adjust ourselves without suffering to most of these conditions. But such adjustment is far from being a victorious adaptation. It brings about organic and mental changes, which are equivalent to a degradation of civilized man.

   Permanent modifications of body and consciousness may be produced by adaptation. In this manner, environment stamps human beings with its mark. When young people are subjected to its influence over lengthy periods, they may be indelibly modified by it. Thus, new structural and mental aspects appear in the individual and also in the race. It seems that environment gradually affects the cells of the sexual glands. Such modifications are naturally hereditary. Indeed, the individual does not transmit his acquired characteristics to his descendants. But when in the course of life his humors are modified by the environment, his sexual tissues may adapt themselves, by corresponding structural changes, to the state of their humoral medium. For instance, the plants, trees, animals, and men of Normandy differ greatly from those of Brittany. They bear the specific mark of the soil. In former times, when the food of the inhabitants of a village consisted exclusively of local products, the aspect of the population showed still greater differences from one province to another.

   Adaptation of animals to thirst and to hunger is easily noticeable. The cattle of the Arizona deserts can go three or four days without water. A dog may remain fat and in perfect health, although eating only twice a week. Animals unable to quench their thirst except at rare intervals learn to drink abundantly. They adapt their tissues to store large quantities of water over lengthy periods. Likewise, those subjected to fasting become accustomed to absorbing in one or two days enough food for the rest of the week. It is the same with sleep. We can train ourselves to do without sleep, or to sleep very little during some periods, and a great deal during others. We indulge quite easily in an excess of nourishment and of drink. If a child is given as much food as he can absorb, he rapidly gets used to eating exaggerated quantities. Later on, he finds it very difficult to break himself of the habit. All the organic and mental consequences of alimentary excesses are not yet exactly understood. They seem to be manifested by an increase in the volume and the height of the body, and by a decrease in its general activity. A similar phenomenon occurs in wild rabbits when they become transformed into domestic rabbits. It is not certain that the standardized habits of modern life lead to the optimum development of human beings. The present ways of living have been adopted because they are easy and pleasant. Indeed, they differ profoundly from those of our ancestors and of the human groups which have so far resisted industrial civilization. We do not know, as yet, whether they are better or worse.

   Man becomes acclimatized to high altitudes through certain modifications of his blood and of his circulatory, respiratory, skeletal, and muscular systems. The red corpuscles respond to the lowering of the barometric pressure by multiplying. Adaptation rapidly takes place. In a few weeks, soldiers transported to the summits of the Alps walk, climb, and run as actively as at lower altitudes. At the same time, the skin produces a great deal of pigment as a protection against the glare of the snow. The thorax and the muscles of the chest develop markedly. After some months in the high mountains, the muscular system is inured to the greater efforts required for active life. The shape and the posture of the body become modified. The circulatory apparatus and the heart accustom themselves to the ceaseless work they are called upon to do. The processes that regulate the temperature of the blood improve. The organism learns to resist cold and to support easily all inlemencies of the weather. When mountaineers descend to the plains, the number of their blood corpuscles becomes normal. But the adaptation of the thorax, lungs, heart, and vessels to a rarefied atmosphere, to the effects of cold, to the exertions made in the daily ascension of mountains, leaves its mark forever on the body. Intense muscular activity also brings about permanent changes. For example, on the Western ranches, the cowpunchers acquire strength, resistance, and litheness such as no athlete ever attains in the comfort of a modern university. It is the same with intellectual work. Man is indelibly marked by prolonged and intense mental struggle. This type of activity is almost impossible in the state of mechanization reached by education. It can only take place in small groups, such as that of the first disciples of Pasteur, inspired by an ardent ideal, by the will to know. The young men who gathered around Welch, at the beginning of his career at the Johns Hopkins University, have been strengthened during their whole lives and made greater by the intellectual discipline into which they were initiated under his guidance.

   There is also a more subtle, less known aspect of the adaptation of organic and mental activities to environment. It consists of the response of the body to the chemical substances contained in the food. We know that in countries where water is rich in calcium, the skeleton becomes heavier than it does in regions where the water is quite pure. We also know that individuals fed on milk, eggs, vegetables, and cereals differ from those fed mostly on meat, that many substances may influence the shape of the body and consciousness. But we ignore the mechanism of this adaptation. Endocrine glands and nervous system probably become modified according to the forms of alimentation. Mental activities seem to vary with the constitution of the tissues. It is not wise to follow blindly the doctrines of physicians and hygienists, whose horizon is limited to their specialty--that is, to one aspect of the individual. The progress of man certainly will not come from an increase in weight, or in longevity.

   It seems that the work of the adaptive mechanisms stimulates all organic functions. A temporary change of climate is of benefit to debilitated individuals and to convalescents. Some variations in the mode of life, in food, sleep, and habitat, are useful. The accomodation to new conditions of existence momentarily increases the activity of physiological and mental processes. The rate of adaptation to any factor depends on the rhythm of physiological time. Children respond immediately to a change of climate. Adults, much more slowly. In order to produce lasting results, the action of the environment must be prolonged. During youth, a new country and new habits are able to determine permanent adaptive changes. For this reason, conscription greatly helps the development of the body by imposing on each individual a new type of life, certain exercises, and a certain discipline. Rougher conditions of existence and more responsibility would restore moral energy and audacity to the majority of those who have lost them. More virile habits should be substituted for the uniformity and softness of life in schools and universities. The adaptation of the individual to a physiological, intellectual, and moral discipline determines definite changes in the nervous system, the endocrine glands, and the mind. The organism acquires, in this way, a better integration, greater vigor, and more ability to overcome the difficulties and dangers of existence.

   Man adapts himself to social environment as to physical environment. Mental activities, like physiological activities, tend to become modified in the way best suited to the survival of the body. They determine our adjustment to our surroundings. The individual does not generally get without effort the position he covets in the group of which he is a member. He wants wealth, knowledge, power, pleasures. He is driven by his greed, his ambition, his curiosity, his sexual appetite. But he finds himself in an environment always indifferent, sometimes hostile. He quickly realizes that he must fight for what he wants. His mode of reaction to his social surroundings depends on his specific constitution. Some people become accommodated to the world by conquering it. Others by escaping from it. Still others refuse to accept its rules. The natural attitude of the individual toward his fellow men is one of strife. Consciousness responds to the enmity of the environment by an effort directed against it. Intelligence and cunning then develop, as well as the desire to learn, the will to work, to possess, and to dominate. The passion for conquest assumes diverse aspects according to individuals and circumstances. It inspires all great adventures. Such passion led Pasteur to the renovation of medicine, Mussolini to the building up of a great nation, Einstein to the creation of a universe. The same spirit drives the modern human being to robbery, to murder, and to the great financial and economic enterprises characterizing our civilization. But its impulse also builds hospitals, laboratories, universities, and churches. It impels men to fortune and to death, to heroism and to crime. But never to happiness.

   The second mode of adaptation is flight. Some abandon the struggle and descend to a social level where competition is no longer necessary. They become factory workers, proletarians. Others take refuge within their own self. At the same time they can adapt themselves, in some measure, to the social group, and even conquer it through the superiority of their intelligence. But they do not fight. They are members of the community only in appearance. In fact, they live in an inner world of their own. Still others forget their surroundings in ceaseless toil. Those who are obliged to work uninterruptedly accommodate themselves to all events. A woman whose child dies, and who has to look after several other children, has no time to brood over her grief. Work is more effective than alcohol and morphine in helping people to bear adverse conditions. Certain individuals spend their lives in dreaming, in hoping for fortune, health, and happiness. Illusions and hope are also a powerful means of adaptation. Hope generates action. It is rightly looked upon by Christian morals as a great virtue. It contributes in a powerful manner to the adjustment of the individual to unfavorable circumstances. Habit is another aspect of adaptation. Sorrows are more quickly forgotten than joys. But inaction augments all sufferings.

   Many people never adjust themselves to the social group. Among those unadapted are the feeble-minded. Except in special institutions, they have no place in modern society. A number of normal children are born in the families of degenerates and criminals. In such a mold they shape their body and their consciousness. They become unadaptable to normal life. They supply the prisons with most of their inmates. They also constitute the far larger population that remains free to live by burglary and murder. These human beings are the fatal result of physiological and moral degradation brought about by industrial civilization. They are irresponsible. Irresponsible, also, is the youth brought up in modern schools by teachers ignorant of the necessity for effort, for intellectual concentration, for moral discipline. Later on in life, when these young men and women encounter the indifference of the world, the material and mental difficulties of existence, they are incapable of adaptation, save by asking for relief, for protection, for doles, and, if relief cannot thus be obtained, by crime. Although having strong muscles, they are deprived of nervous and moral resistance. They shrink from effort and privation. In periods of stress they demand food and shelter from their parents or from the community. Like the offspring of the wretched and the criminals, they are unfit to have a place in the new city.

   Certain forms of modem life lead directly to degeneration. There are social conditions as fatal to white men as are warm and humid climates. We react to poverty, anxieties, and sorrows by working and struggling. We can stand tyranny, revolution, and war. But we are not able to fight successfully against misery or prosperity. The individual and the race are weakened by extreme poverty. Wealth is just as dangerous. Nevertheless, there are still families which, in spite of having had money and power for centuries, have kept their strength. But, in former times, power and money derived from the ownership of land. To hold the land required struggle, administrative ability, and leadership. This indispensable effort prevented degeneration. Today, wealth does not bring in its train any responsibility toward the community. Irresponsibility, even in the absence of wealth, is harmful. In the poor, as well as in the rich, leisure engenders degeneration. Cinemas, concerts, radios, automobiles, and athletics are no substitutes for intelligent work. We are far from having solved this momentous problem of idleness created by prosperity, modern machinery, or unemployment. By imposing leisure upon man, scientific civilization has brought him great misfortune. We are as incapable of fighting the consequences of indolence and irresponsibility as cancer and mental diseases.

   Adaptive functions assume as many different aspects as tissues and humors encounter new situations. They are not the particular expression of any organic system. They are definable only by their end. Their means vary. But their end always remains the same. Such an end is the survival of the individual. Adaptation, considered in its various manifestations and its oneness, appears as an agent of stabilization and organic repair, as the cause of the molding of organs by function, as the link that integrates tissues and humors in a whole enduring in spite of the attacks of the outer world. Thus, it appears as an entity. This abstraction is convenient for describing its characteristics. In fact, adaptation is an aspect of all physiological processes and of their physicochemical components.

   When a system is in equilibrium, and a factor tends to modify the equilibrium, there occurs a reaction that opposes this factor. If sugar is dissolved in water, the temperature falls, and the lowering of the temperature diminishes the solubility of sugar. Such is the principle of Le Chatelier. When violent muscular exercise greatly increases the quantity of venous blood flowing into the heart, the central nervous system is informed of this event by the nerves of the right auricle. At once it determines an acceleration of the cardiac pulsations. The excess of venous blood is thus carried away. There is only a superficial analogy between the principle of Le Chatelier and such physiological adaptation. In the first case, an equilibrium is maintained by physical means. In the second case, a steady state, and not an equilibrium, persists with the help of physiological processes. If, instead of blood, a tissue modifies its state, a similar phenomenon occurs. The extirpation of a fragment of skin sets in motion a complex reaction which, through converging mechanisms, brings about the repair of the lesion. In both instances, the excess of venous blood and the wound are the factors tending to modify the state of the organism. These factors are opposed by a concatenation of physiological processes leading, in the first case, to acceleration of the heart and, in the second case, to cicatrization.

   The more a muscle works, the more it develops. Activity strengthens it, instead of wearing it out. An organ atrophies when not used. It is a primary datum of observation that physiological and mental functions are improved by work. Also, that effort is indispensable to the optimum development of the individual. Like muscles and organs, intelligence and moral sense become atrophied for want of exercise. The law of effort is still more important than the law of the constancy of the organic states. Steadiness of the inner medium is, without any doubt, indispensable to the survival of the organism. But the physiological and mental progress of the individual depends on his functional activity and on his efforts. We become adapted to the lack of use of our organic and mental systems by degenerating.

   Adaptation employs multiple processes to attain its end. It never localizes in one region or one organ. It mobilizes the entire body. For example, anger profoundly modifies all the organic apparatuses. The muscles contract. The sympathetic nerves and the suprarenal glands come into action. Their intervention brings about an increase of the blood pressure, an acceleration of the heart pulsations, the setting free by the liver of glucose, which will be used by the muscles as fuel. In a like manner, when the body strives against outside cold, its circulatory, respiratory, digestive, muscular, and nervous apparatuses are forced to act. In sum, the organism responds to changes in the outer world by setting in motion all its activities. The exercise of adaptive functions is as necessary to the development of body and consciousness as physical effort to that of the muscles. Accommodation to inclemency of the weather, to lack of sleep, to fatigue, and to hunger stimulates every physiological process. In order to reach his optimum state, the human being must actualize all his potentialities.

   Adaptive phenomena always tend toward a certain end. But they do not always attain their goal. They do not work accurately. They operate within certain limits. Each individual withstands only a given number of bacteria and a given virulence of these bacteria. Beyond such number and virulence, the adaptive functions become insufficient to protect the body. Disease breaks out. It is the same with resistance to fatigue, to heat, or to cold. There is doubt that adaptive power, as well as other physiological activities, increases with exercise. Like these activities, it is perfectible. Instead of preventing diseases only by protecting the individual against their agents, we must, by artificially increasing the efficiency of his adaptive functions, render each man capable of protecting himself.

   To summarize. We have considered adaptation as an expression of fundamental properties of the tissues, as an aspect of nutrition. Physiological processes are modified in as many different ways as new and unforeseen situations occur. Strange to say, they shape themselves for the goal to be attained. They do not seem to estimate time and space in the same manner as our intelligence does. The tissues organize with equal ease relative to spatial configurations already existing and to those which do not as yet exist. During embryonic growth, the retina and the lens associate for the benefit of the still potential eye. Adaptability is a property of the components of tissues, as well as of the tissues themselves and of the entire organism. Individual cells appear to act in the interest of the whole, just as bees work for the good of the hive. They seem to know the future. And they prepare for this future by anticipated changes of their structure and functions.

   We utilize our adaptive functions much less than our ancestors did. For a quarter of a century, especially, we have accommodated ourselves to our environment through mechanisms created by our intelligence, and no longer through physiological mechanisms. Science has supplied us with means for keeping our intraorganic equilibrium, which are more agreeable and less laborious than the natural processes. We have mentioned how the physical conditions of our daily life are prevented from varying. How muscular exercise, food, and sleep are standardized. How modern civilization has done away with effort and moral responsibility, and transformed the modes of activity of our muscular, nervous, circulatory, and glandular systems.

   We have also drawn attention to the fact that the inhabitants of the modern city no longer suffer from changes of atmospheric temperature. That they are protected by modern houses, clothes, and automobiles. That during the winter they are not subjected, as their ancestors were, to alternatives of prolonged cold and of brutal heat from stoves and open fireplaces. The organism does not have to fight cold by setting in motion the chain of the associated physiological processes, which increase the chemical exchanges and modify the circulation of all the tissues. When an individual, insufficiently clothed, has to maintain his inner temperature by violent exercise, all his organic systems work with great intensity. On the contrary, these systems remain in a condition of repose if cold weather is fought by furs and warm clothing, by the heating apparatus of a closed car, or by the walls of a steam-heated room. The skin of modern man is never whipped by the wind. It never has to defend itself for long and tiring hours against snow, rain, or sun. In former times the mechanisms responsible for regulating the temperature of blood and humors were maintained in constant activity by the struggle against the rigors of the weather. Today they are in a state of perpetual rest. However, their work is probably indispensable to the optimum development of the body and the mind. We must realize that the adaptive functions do not correspond to a particular structure which, when not needed, could be dispensed with. They are, on the contrary, the expression of the whole body.

   Muscular effort has not been completely eliminated from modern life, but it is not frequent. It has been replaced in our daily existence by that of machines. Muscles are now used only in athletic games. Their mode of acting is standardized and subjected to arbitrary rules. It is doubtful whether these artificial exercises completely replace the hardships of a more primitive condition of life. For women, dancing and playing tennis for a few hours every week are not the equivalent of the effort required to climb up and down stairs, to carry out their domestic duties without the help of machines, to walk along the streets. Nowadays, they live in houses provided with an elevator, walk with difficulty on high heels, and almost constantly use an automobile or a trolley car. It is the same with men. Golf on Saturdays and Sundays does not compensate for the complete inaction of the rest of the week. By doing away with muscular effort in daily life, we have suppressed, without being aware of it, the ceaseless exercise required from our organic systems in order that the constancy of the inner medium be maintained. As is well known, muscles, when they work, consume sugar and oxygen, produce heat, and pour lactic acid into the circulating blood. To adapt itself to these changes, the organisms must set in action the heart, the respiratory apparatus, the liver, the pancreas, the kidneys, the sweat glands, and the cerebrospinal and sympathetic systems. In sum, the intermittent exercises of modern man, such as golf and tennis, are not equivalent to the continuous muscular activity required by the existence of our ancestors. Today, physical effort only takes place at certain moments and on certain days. The customary state of the organic systems, of blood vessels, of sweat and endocrine glands, is that of repose.

   The usage of the digestive functions has also been modified. Hard foods, such as stale bread or tough meat, are no longer permitted in our diet. Likewise, physicians have forgotten that jaws are made to grind resistant matter, and that the stomach is constructed to digest natural products. As previously mentioned, children are fed chiefly on soft, mashed, pulped food, and milk. Their jaws, their teeth, and the muscles of their face are not subjected to sufficiently hard work. It is the same with the muscles and glands of their digestive apparatus. The frequency, the regularity, and the abundance of meals render useless an adaptive function that has played an important part in the survival of human races, the adaptation to lack of food. In primitive life men were subjected to long periods of fasting. When want did not compel them to starve, they voluntarily deprived themselves of food. All religions have insisted upon the necessity of fasting. Privation of food at first brings about a sensation of hunger, occasionally some nervous stimulation, and later a feeling of weakness. But it also determines certain hidden phenomena which are far more important. The sugar of the liver, the fat of the subcutaneous deposits, are mobilized, and also the proteins of the muscles and the glands. All the organs sacrifice their own substances in order to maintain blood, heart, and brain in a normal condition. Fasting purifies and profoundly modifies our tissues.

   Modern man sleeps too much or not enough. He does not easily adapt himself to too much sleep. He fares still worse if he sleeps too little during prolonged periods. It is, however, useful to accustom oneself to remain awake when one wants to sleep. The struggle against sleep sets in motion organic apparatuses whose strength develops by exercise. It also calls for an effort of the will. This effort, together with many others, has been suppressed by modem habits. In spite of the restlessness of existence, the false activity of sports and rapid transportation, the great organic systems responsible for our adaptive functions remain idle. In short, the mode of life created by scientific civilization has rendered useless a number of mechanisms whose activities had never ceased during the millenniums of the existence of the human race.

   The exercise of the adaptive functions appears to be indispensable to the optimum development of man. Our body is placed in a physical medium whose conditions are variable. The constancy of our inner states is maintained through ceaseless organic activity. Such activity is not localized in a single system. It extends to the entire body. All our anatomical apparatuses react against the outside world in the sense most favorable to our survival. Is it possible that such a fundamental property may remain virtual without inconvenience to our body? Are we not organized to live under changing and irregular conditions? Man attains his highest development when he is exposed to the rigors of the seasons, when he sometimes goes without sleep and sometimes sleeps for long hours, when his meals are sometimes abundant and sometimes scanty, when he conquers food and shelter at the price of strenuous efforts. He has also to train his muscles, to tire himself and rest, to fight, suffer, and be happy, to love and to hate. His will needs alternately to strain and to relax. He must strive against his fellow men or against himself. He is made for such an existence, just as the stomach is made for digesting food. When his adaptive processes work most intensely, he develops his virility to the fullest extent. It is a primary datum of observation that hardships make for nervous resistance and health. We know how strong physically and morally are those who, since childhood, have been submitted to intelligent discipline, who have endured some privations and adapted themselves to adverse conditions.

   However, we observe human beings who develop fully even though they are not obliged by poverty to fight against their environment. But these individuals are also molded by adaptation, although in a different way. Generally, they have imposed upon themselves, or have accepted from others, a discipline, a sort of asceticism, which has protected them against the deleterious effects of wealth and leisure. The sons of feudal lords were subjected to a hard physical and moral training. One of Brittany's heroes, Bertrand du Guesclin, compelled himself every day to face the inclemencies of the weather and to fight with children of his own age. Although small and ill-formed, he acquired such endurance and strength as are still legendary. During the early period of the development of the United States, the men who built the railroads, laid the foundations of the large industries, and opened the West to civilization, triumphed over all obstacles by their will and their audacity. Today most of the sons of these great men possess wealth, without having had to earn it. They have never struggled against their environment. Generally, they lack the ancestral strength. A similar phenomenon occurred in Europe among the descendants of the feudal aristocracy and of the great financiers and manufacturers of the nineteenth century.

   The effect of the deficiencies of adaptation upon the development of man is not as yet completely known. In the large cities, there are many individuals whose adaptive activities are permanently at rest. Sometimes the consequences of this phenomenon become obvious. They manifest themselves especially in the children of rich families. And, likewise, in those who are brought up in the same way as the rich. From their birth, these children live under conditions that bring about the atrophy of their adaptive systems. They are kept in warm rooms and, when they go out, dressed like little Eskimos. They are crammed with food, they sleep as much as they like, have no responsibility, never make an intellectual or moral effort, learn only what amuses them, and struggle against nothing. The result is well known. They generally become pleasant and handsome, often strong, easily tired, extremely selfish, without intellectual acuteness, moral sense, and nervous resistance. These defects are not of ancestral origin. They are observed in the descendants of the men who built up American industries, as well as in those of the newcomers. Obviously, a function as important as adaptation cannot be left in disuse with impunity. The law of the struggle for life must, above all, be obeyed. Degeneration of body and soul is the price paid by the individuals and the races who have forgotten the existence of this law.

   As optimum development requires the activity of all organic systems, a decrease in the value of man necessarily follows the decay of the adaptive functions. In the process of education, these functions must be kept constantly at work. Each one of them is equally useful. Muscles are no more important than brains. They only contribute strength and harmony to the body. Instead of training athletes, we have to construct modern men. And modern men need more nervous resistance, intelligence, and moral energy than muscular power. The acquisition of these qualities calls for effort, struggle, and discipline. It also demands that human beings should not be exposed to conditions of existence to which they are unadaptable. Apparently, there is no adaptation possible to ceaseless agitation, intellectual dispersion, alcoholism, precocious sexual excesses, noise, polluted air, and adulterated foods. If such is the case, we must modify our mode of life and our environment, even at the cost of a destructive revolution. After all, the purpose of civilization is not the progress of science and machines, but the progress of man.

   In conclusion. Adaptation is a mode of being of all organic and mental processes. It is not an entity. It is equivalent to the automatic grouping of our activities in such a manner as to assure the survival of the individual. It is essentially teleo-logical. Owing to the adaptive activities, the organic medium remains constant, the body conserves its unity and recovers from diseases. It is for the same reason that we endure, in spite of the fragility and the transitory character of our tissues. Adaptation is as indispensable as nutrition. In fact, it is only an aspect of nutrition. However, in the organization of modem life no account has ever been taken of such an important function. Its use has been almost completely given up. And this neglect has brought about a deterioration of the body and of the mind.

   This mode of activity is necessary to the complete development of the human being. Its deficiency determines the atrophy of the nutritive and mental functions from which it is not distinct. Adaptation causes the organic processes to move simultaneously according to the rhythms of physiological time and of the unforeseeable variations of the environment. Any change in the environment elicits a response of all physiological and mental processes. Those movements of the functional systems express the apprehension by man of the outer reality. They act as a buffer for the material and psychological shocks which he unceasingly receives. They not only permit him to endure, but they also are the agents of his formation and of his progress. They are endowed with a property of capital importance. The property of being easily modified by certain chemical, physical, and psychological factors, which we know well how to handle. We can use these factors as tools, and thus successfully intervene in the development of human activities In fact, the knowledge of the mechanisms of adaptation gives man the power of renovating and of constructing himself.

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