Man the Unknown
The human body is placed, on the scale of magnitudes, halfway between the atom and the star. According to the size of the objects selected for comparison, it appears either large or small. Its length is equivalent to that of two hundred thousand tissue cells, or of two millions of ordinary microbes, or of two billions of albumin molecules, placed end to end. Man is gigantic in comparison with an electron, an atom, a molecule, or a microbe. But, when compared with a mountain, or with the earth, he is tiny. More than four thousand individuals would have to stand one upon the other in order to equal the height of Mount Everest. A terrestrial meridian is approximately equivalent to twenty millions of them placed end to end. Light, as is well known, travels about one hundred and fifty million times the length of our body in one second. The interstellar distances are such that they have to be measured in light years.1 Our stature, in relation to such a system of reference, becomes inconceivably small.... In reality, our spatial greatness or smallness is without importance. For what is specific of man has no physical dimensions. The meaning of our presence in this world assuredly does not depend upon our size...
Each man is characterized by his figure, his way of carrying him self, the aspect of his face. Our outward form expresses the qualities, the powers, of our body and our mind. In a given race, it varies according to the mode of life of the individuals. The man of the Renaissance, whose life was a constant fight, who was exposed continuously to dangers and to inclemencies, who was capable of as great an enthusiasm for the discoveries of Galileo as for the masterpieces of Leonardo da Vinci or Michelangelo, did not resemble modern man who lives in a steam-heated apartment, an air conditioned office, a closed car, who contemplates absurd films, listens to his radio, and plays golf and bridge. Each epoch puts its seal on human beings.... Our form is moulded by our physiological habits, and even by our usual thoughts.
Its characteristics are partly due to the muscles running under the skin or along the bones. The size of these muscles depends on the exercise to which they are submitted. The beauty of the body comes from the harmonious development of the muscles and the skeleton. It reached the height of perfection at the epoch of Pericles, in the Greek athletes whom Phidias and his disciples immortalized in their statues. The shape of the face, the mouth, the cheeks, the eyelids, and the lines of the visage are determined by the habitual condition of the flat muscles, which move in the adipose tissue underlying the skin. And the states of these muscles depends on that of our mind. Indeed, each individual can give his face the expression that he chooses. But he does not keep such a mask permanently. Unwittingly, our visage progressively models itself upon our states of consciousness. With the advance of age it becomes more and more pregnant with the feelings, the appetites, and the aspirations of the whole being. The beauty of youth comes from the natural harmony of the lineaments of the human face. That, so rare, of an old man, from his soul.
The visage expresses still deeper things than the hidden activities of consciousness. In this open book one can read not only the vices,
the virtues, the intelligence, the stupidity, the feelings, the most carefully concealed habits, of an individual, but also the constitution of his body, and his tendencies to organic and mental diseases. In fact, the aspect of bones, muscles, fat, skin, and hair depends on the nutrition of tissues. And the nutrition of tissues is regulated by the composition of blood plasma, that is, by the activity of the glandular and digestive systems. The state of the organs is revealed by the aspect of the body. The surface of the skin reflects the functional conditions of the endocrine glands, the stomach, the intestines, and the nervous system. It points out the morbid tendencies of the individual. In fact, people who belong to different morphological classes2 — for instance, to the cerebral, digestive, muscular, or respiratory types — are not liable to the same organic or mental diseases. There are great functional disparities between tall and spare men, and broad and short ones.... In the diagnosis and prognosis of diseases, ancient physicians, quite rightly, attributed great importance to temperament, idiosyncrasies, and diatheses.3 Each man bears on his face the description of his body and his soul.
Adaptive functions are responsible for duration
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 humours. The body seems to mould 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 substratum4 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 extra organic. Intraorganic adaptation is responsible for the constancy of the organic medium and of the relations of tissues and humours. 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 unfavourable 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.
Intraorganic adaptation. Automatic regulation of the volume and composition of blood and humours.
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 humours 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 effort's 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 humours 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 litres 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 lumen5 of the intestine. The administration of a purgative is followed by a similar waste of water. The gains and losses are exactly counter balanced 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 calibre. 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,6 increases the rate of cardiac pulsations, and blood escapes more rapidly from the heart into the vessels. Moreover, serum7 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.8 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.
Organic correlations. Teleological aspect of the phenomenon. Adaptation to future events. Adaptation to haemorrhage. Correlation of the structures of the eye
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 Ideological9. If we attribute to tissues an intelligence of the same kind as ours, as mechanists and vitalists 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 foetus 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 is abundantly provided with factors of safety. In the same way, the extirpation10 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 haemorrhage. 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 re-establishes 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 concatenation11 of physiological, physicochemical, and structural phenomena. These phenomena constitute the adaptation of the whole to haemorrhage.
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 and metamorphoses12 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....
Repair of tissues
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
lesions13 of the tissues. As in blood regeneration, heterogeneous and converging mechanisms come into play. They all turn toward the end to he attained, the reconstruction of the destroyed structures. An artery is cut. Blood gushes in abundance. Arterial pressure is lowered. The patient has a syncope.14 The haemorrhage decreases. A clot forms in the wound. Fibrin15 occludes the opening of the vessel. Then the haemorrhage definitely stops. During the following days, leucocytes16 and tissue 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,17 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 osseous18 and muscular debris. Then, circulation becomes more active. The limb swells. The nutritive sub stances 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 physicochemical 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.
...If one of the regenerating mechanisms fails, it is replaced by the other. The result alone is invariable. And not the procedure. After a haemorrhage, arterial pressure and blood volume are re-established 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....
Extraorganic adaptation. Adaptation to physical environment
Extraorganic adaptation 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 warmer or colder than the skin. Nevertheless, the temperature of the humours 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.19 Consequently, the temperature of the blood in the lungs is lowered. At the same time, the subcutaneous20 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.
The outer and inner surfaces of the body
The skin, which covers the outer surface of the body, is impermeable to water and to gases. It does not allow the microbes living on its surface to enter the organism. It is capable of destroying them with the aid of substances secreted by its glands. But it can be crossed by the minute and deadly beings, which we call viruses. Its external face is exposed to light, wind, humidity, dryness, heat, and cold. Its internal face is in contact with an aquatic world, warm and deprived of light, where cells live like marine animals. Despite its thinness, the skin effectively protects the organic fluids against the unceasing variations of cosmic surroundings. It is moist, supple, extensible, elastic, durable. Its durability is due to its mode of constitution, to its several layers of cells, which slowly and endlessly multiply. These cells die while remaining united to one another like the slates of a roof-like slates ceaselessly blown away by the wind and continually replaced by new slates. The skin, nevertheless, retains its moistness and suppleness, because small glands secrete on its surface both water and fatty substances. At the nostrils, mouth, anus, urethra, and vagina, it joins the mucosas, those membranes that cover the inner surface of the body. All its orifices, with the exception of the nostrils, are closed by elastic and contractile rings, the sphincters. Thus, it is the almost perfectly fortified frontier of a closed world.
Through its outer surface,, the body enters into communication with all the things of the cosmic universe. In fact, the skin is the dwelling place of an immense quantity of small receptor organs, each of which registers, according to its own structure, the changes taking place in the environment. Tactile corpuscles scattered all over its surface are
sensitive to pressure, to pain, to heat, or to cold. Those situated in the mucosa of the tongue are affected by certain qualities of food, and also by temperature. Air vibrations act on the extremely complex apparatus of the internal ear by the medium of the tympanic membrane and the bones of the middle ear. The network of olfactory nerves, which extends into the nasal mucous membrane, is sensitive to odors. A strange phenomenon occurs in the embryo. The brain causes a part of itself, the optic nerve and retina, to shoot out toward the surface of the body.' The part of the skin overlying the young retina undergoes an astonishing modification. It becomes transparent, forms the cornea and the crystalline lens, and unites with other tissues to build up the prodigious optical system which we call the eye. The brain is, thus, enabled to record the electromagnetic waves comprised between red and violet.
Innumerable nerve fibres radiate from all these organs and connect them with the spinal cord and the brain. Through the agency of these nerves the central nervous system spreads like a web over the entire surface of the body where it enters into contact with the outer world. The aspect of the universe depends on the constitution of the sense organs, and on their degree of sensitiveness....
We ignore things which have no action on the nerve endings of the surface of the skin. Therefore, we do not perceive cosmic rays, although they pass right through our body. It seems that everything reaching the brain has to enter the sensory organs – that is, to influence the nervous layer enveloping our body.... The skin and its appendages play the part of a faithful keeper of our organs and our blood. They allow certain things to enter our inner world and exclude others. They are the ever open, though carefully watched, door to our
central nervous system. They must be looked upon as being an essential part of ourselves.
Our internal frontier begins at the mouth and the nose, and ends at the anus. Through these openings the outside world penetrates into the respiratory and digestive systems. While the skin is impervious to water and to gas, the mucous membranes of the lungs and of the intestines allow these substances to pass. They are responsible for the chemical continuity of our body with its surroundings. Our inner surface is far larger than that of the skin. The area covered by the flat cells of the pulmonary alveoli is immense. It is approximately equal to five hundred square meters. The thin membrane formed by these cells is traversed by oxygen from the air and by carbon dioxide from the venous blood. It is easily affected by poisonous gases and by bacteria, and more particularly by pneumococci. Atmospheric air, before reaching the pulmonary alveoli, passes through the nose, the pharynx, the larynx, the trachea, and the bronchi, where it is moistened and freed from dust and microbes....
From mouth to anus, the body is traversed by a stream of nutritive substances. The digestive membranes determine the nature of the chemical relations between the external world and the inner world of our tissues and organic fluids. But their functions are far more complex than those of the respiratory ones. They must profoundly transform the food stuffs which reach their surface. They are not only a filter, but also a chemical factory. The ferments secreted by their glands collaborate with those of the pancreas in decomposing the aliments into substances capable of being absorbed by the intestinal cells. The digestive surface is extraordinarily vast. The mucosas secrete and absorb large quantities of fluids. Their cells allow the foodstuffs, when digested, to enter the body.... The soundness of the respiratory and digestive membranes governs, in a large measure, the resistance of the organism to infectious diseases, its strength, its equilibrium, its effectivity, its intellectual attitude.
Thus, our body constitutes a closed universe,' limited on one side by the skin, and on the other by the mucosas covering our inner surfaces. If these membranes are impaired at any point, the existence of the individual is endangered. Even a superficial burn, when extending over a large area of the skin, results in death. This covering separates our organs and humours from the cosmic environment, and yet allows most
extensive physical and chemical communications between these two worlds. It accomplishes the miracle of being a barrier at once closed and open....
The constitution of the body. Cells and their societies. Their structure. Cell types
The inside of our body does not resemble the descriptions of classical anatomy. This science has constructed a schema of the human being that is purely structural and quite unreal. It is not merely by opening a corpse that one may learn how man is constituted. Of course, we can observe in this way his framework, the skeleton and the muscles, which are the scaffold of the organs. In a cage formed by the spinal column, the ribs, and the sternum, are suspended the heart and the lungs. The liver, spleen, kidneys, stomach, intestines, and sexual glands are attached, by the folds of the peritoneum, to the inner surface of a large cavity whose bottom is formed by the pelvis, the sides by the abdominal muscles, and the roof by the diaphragm. The most fragile of all the organs, the brain and the cord, are enclosed in osseous boxes, the cranium and the spine. They are protected against the hardness of the walls of their lodgings by a system of membranes and a cushion of liquid.
One cannot understand the living being by studying a dead body. For the tissues of a corpse have been deprived of their circulating blood and of their functions. In reality, an organ separated from its nutritive medium no longer exists. In the living body, blood is present every where. It pulsates in the arteries, glides through the veins, fills the capillary vessels, bathes all tissues in transparent lymph....21
Within the body, the cells behave like small organisms plunged in an aerated and nutritive medium. This medium is analogous to sea water. However, it contains a smaller quantity of salts, and its composition is much richer and more varied. The leucocytes of the blood and the cells covering the walls of blood vessels and lymphatics are like fish swimming freely in the depth of the ocean or lying flat on the sandy bottom. But the cells forming the tissues do not float in a fluid. They are comparable, not to fish, but to amphibia inhabiting marshes or moist sand. All living cells depend absolutely on the medium in which they are immersed. They modify this medium unceasingly, and are modified by it. In fact, they are inseparable from it. As inseparable
as their body is from its nucleus. Their structure and functions are entirely subordinated to the physical, physicochemical, and chemical conditions of the surrounding fluid. This fluid is the interstitial lymph which at once produces, and is produced by, blood plasma. Cells and medium, structure and function, cannot be separated from one another. The isolation of cells from their natural environment is altogether unwarranted. However, methodological necessity forces us to divide this ensemble into fragments, and to describe, on one side, the cells and tissues, and, on the other, the organic medium – that is, the blood and the humours.
Blood and organic medium
The organic medium is a part of the tissues. Should it be removed, the body would cease to exist. Every manifestation of the life of our organs and nervous centres, our thoughts, our affections, the cruelty, the ugliness, and the beauty of the universe, its very existence, depend on the physicochemical state of our humours. The organic medium is composed of blood, flowing in the vessels, and of fluids, plasma or lymph, which filter through the walls of the capillaries into the tissues. There is a general organic medium, the blood, and regional media, consisting of the interstitial22 lymph of each organ. An organ may be compared to a pond completely filled with aquatic plants and fed by a small brook. The almost stagnant water is polluted by waste products, dead fragments of plants, and chemical substances set free by them. The degree of stagnation and of pollution of the water depends on the rapidity and the volume of the brook. Such is the case with interstitial lymph. In short, the composition of the regional media inhabited by the various cells of the body rests, directly or indirectly, on blood.
The blood is a tissue, like all the other tissues. It is composed of about twenty-five or thirty thousand billions of red cells, and of fifty billions of white cells. But these cells are not, like those of the other tissues, immobilized in a framework. They are suspended in a viscous liquid, the plasma. Blood is a moving tissue finding its way into all parts of the body. It carries to each cell the proper nourishment. Acting, at the same time, as a main sewer that takes away the waste products set free by living tissues. It also contains chemical substances and cells capable of repairing organs wherever necessary. These properties are indeed strange. When carrying out such astonishing duties, the blood
stream behaves like a torrent which, with the help of the mud and the trees drifting in its stream, would set about repairing the houses situated on its banks.
Nutrition of tissues. Metabolism
Between the liquids composing the organic medium, and the world of tissues and organs, there are perpetual chemical exchanges. Nutritive activity is a mode of being of the cells, as fundamental as structure and form. As soon as their chemical exchanges, or metabolism, cease, the organs come into equilibrium with their medium and die. Nutrition is synonymous with existence. Living tissues crave oxygen and take it from blood. This means, in physicochemical terms, that they possess a high reducing potential, that a complex system of chemical substances and of ferments enables them to use atmospheric oxygen for energy producing reactions. From the oxygen, hydrogen, and carbon supplied by sugars and fats, living cells procure the mechanical energy necessary for the maintenance of their structure and for their movements, the electrical energy manifesting itself in every change of the organic conditions, and the heat indispensable to chemical reactions and physiological processes. They also find in blood plasma the nitrogen, sulphur, phosphorus, etc., which they utilize for the construction of new cells, and in the processes of growth and repair. With the help of their ferments they divide the proteins, sugars, and fats contained in their medium into smaller and smaller fragments, and make use of the energy so liberated. They simultaneously build up, by means of energy-absorbing reactions, certain compounds,, more complex and having a higher energy potential, and they incorporate them in their own substance.
The intensity of chemical exchanges in the cell communities, or in the entire being, expresses the intensity of organic life. Metabolism is measured by the quantity of oxygen absorbed and that of carbonic acid produced, when the body is in a state of complete repose. This is called basal metabolism. There is a great increase in the activity of the exchanges as soon as muscles contract and perform mechanical work. Metabolism is higher in a child than in an adult, in a mouse than in a dog. Any very large increase in the stature of human beings would probably be followed by a decline of basal metabolism. Brain, liver, and endocrine glands need a great deal of chemical energy. But muscular exercise raises the intensity of the exchanges in the most marked
manner. Nevertheless, all our activities cannot be expressed in chemical terms. Intellectual work, strange to say, does not increase metabolism. It seems to require no energy, or to consume a quantity of it too small to be detected by our present techniques. It is, indeed, an astonishing fact that human thought, which has transformed the surface of the earth, destroyed and built nations, discovered new universes in the immensity of the sidereal23 spaces, is elaborated without demanding a measurable amount of energy. The mightiest effort of our intelligence has incomparably less effect on metabolism than the contraction of the biceps when this muscle lifts a weight of a few grams. The ambition of Caesar, the meditation of Newton, the inspiration of Beethoven, the passionate contemplation of Pasteur, did not modify the chemical exchanges of these great men as much as a few bacteria or a slight stimulation of the thyroid gland would easily have done....
Circulatory apparatus, lungs, and kidneys
In the course of the chemical exchanges, waste products, or catabolites are set free by tissues and organs. They tend to accumulate in the regional medium and to render it uninhabitable for the cells. The phenomenon of nutrition, therefore, requires the existence of apparatuses capable of assuring, through a rapid circulation of lymph and blood, the replacement of the nutritive substances used by the tissues, and the elimination of waste products. The volume of the circulating fluids, compared with that of the organs, is very small. The weight of blood of a human being is hardly equal to one-tenth of his total weight. However, living tissues consume large amounts of oxygen and glucose. They also liberate into the inner medium considerable quantities of carbonic, lactic, hydrochloric, phosphoric acids, etc. A fragment of living tissue, cultivated in a flask, must be given a volume of liquid equal to two thou sand times its own volume, in order not to be poisoned within a few days by its waste products. In addition, it requires a gaseous atmosphere at least ten times larger than its fluid medium. Consequently, a human body reduced to pulp and cultivated in vitro24 would demand about two hundred thousand litres of nutritive fluid. It is on account of the marvellous perfection of the apparatuses responsible for the circulation of the blood, its wealth of nutritive substances, and the constant elimination of the waste products, that our tissues can live in six or seven litres of fluid, instead of two hundred thousand.
Blood maintains its composition constant by perpetually passing through apparatuses where it is purified and recuperates the nutritive sub stances removed by the tissues. When venous blood returns from the muscles and the organs, it is full of carbonic acid and waste products of nutrition. The pulsations of the heart then drive it into the immense network of the lung capillaries, where each red corpuscle comes into con tact with atmospheric oxygen. This gas, in conformity with certain simple physicochemical laws, penetrates the blood and is taken up by the haemoglobin of the red cells. Carbon dioxide simultaneously escapes into the bronchi, whence it is expelled into the outside atmosphere by the respiratory movements. The more rapid the respiration, the more active are the chemical exchanges between air and blood. But during its passage through the lungs, blood gets rid of carbonic acid only. It still contains nonvolatile acids, and all other waste products of metabolism. Its purification is completed during its passage through the kidneys. The kidneys separate from the blood certain substances that are eliminated in the urine. They also regulate the quantity of salts indispensable to plasma in order that its osmotic25 tension may remain constant. The functioning of the kidneys and of the lungs is of a prodigious efficiency. It is the intense activity of these viscera that permits the fluid medium required by living tissues to be so limited, and the human body to possess such compactness and agility.
Physical relations of the body with its environment Voluntary nervous system. Skeletal and muscular systems
...Brain and spinal cord, with nerves and muscles, constitute an indivisible system. Muscles, from a functional point of view, are only a part of the brain. It is with their help and that of the bones that human intelligence has put its mark on the world. Man has been given power over his environment by the shape of his skeleton. The limbs consist of articulated levers, composed of three segments. The upper limb is mounted upon a mobile plate, the shoulder blade, while the osseous girdle, the pelvis, to which the lower limb is jointed, is almost rigid and immobile. The motive muscles lie along the bones. Near the extremity of the arm, these muscles resolve into tendons, which move the fingers and the hand itself. The hand is a masterpiece. Simultaneously, it feels and it acts. It acts as if endowed with sight. Owing to the unique properties of its skin, its tactile nerves, its muscles, and its bones, the hand is capable of manufacturing arms and tools.
We never would have acquired our mastery over matter without the aid of our fingers, those five small levers, each composed of three articulated segments, which are mounted upon the metacarpus and the bones of the wrist. The hand adapts itself to the roughest work as well as to the most delicate. It has wielded with equal skill the flint knife of the primitive hunter, the black smith's hammer, the woodcutter's axe, the farmer's plough, the sword of the medieval knight, the controls of the modern aviator, the artist's brush, the journalist's pen, the threads of the silk-weaver. It is able to kill and to bless, to steal and to give, to sow grain on the surface of the fields and to throw grenades in the trenches. The elasticity, strength, and adaptiveness of the lower limbs, whose pendulum-like oscillations determine walking and running, have never been equated by our machines, which only make use of the principle of the wheel. The three levers, articulated on the pelvis, adapt themselves with marvellous suppleness to all postures, efforts, and movements. They carry us on the polished floor of a ballroom and in the chaos of the ice-fields, upon the sidewalks of Park Avenue and on the slopes of the Rocky Mountains. They enable us to walk, to run, to fall, to climb, to swing, to wander all over the earth under all conditions.
There is another organic system composed of cerebral substance, nerves, muscles, and cartilages, which, to the same degree as the hand, has determined the superiority of man over all living beings. It consists of the tongue and the larynx, and their nervous apparatus. Owing to this system we are capable of expressing our thoughts, of communicating with our fellow men by means of sounds. Were it not for language, civilization would not exist. The use of speech, like that of the hand, has greatly aided the development of the brain. The cerebral parts of the hand, the tongue, and the larynx extend over a large area of the brain surface. At the same time that the nervous centres control writing, speaking, and the grasping and handling of objects, they are, in return, stimulated by these acts. Simultaneously, they are determining and
determined. It seems that the work of the mind is helped by the rhythmic contractions of the muscles. Certain exercises appear to stimulate thought. For this reason, perhaps, Aristotle and his disciples were in the habit of walking while discussing the fundamental problems of philosophy and science. No part of the nervous centres seems to act separately. Viscera, muscles, spinal cord, cerebrum, are functionally one. Skeletal muscles, for their coordinated action, depend on brain and spinal cord, and also on many organs. They receive their orders from the central nervous system, and their energy from the heart, the lungs, the endocrine glands, and the blood. To carry out the directions of the brain, they demand the help of the whole body.
Complexity and simplicity of the body. Structural and functional limits of organs. Anatomical heterogeneity and physiological homogeneity
The body thus appears as an extremely complex thing, a stupendous association of different cell races, each race comprising billions of individuals. These individuals live immersed in humours made of chemical substances, which are manufactured by the organs, and of other sub stances derived from food. From one end of the body to the other, they communicate by chemical messengers — that is, by the agency of their secretions. Moreover, they are united by the nervous system. Their associations, as revealed by scientific techniques, are of an enormous complexity. Nevertheless, these immense crowds of individuals behave like a perfectly integrated being. Our acts are simple. For example, the act of accurately estimating a minute weight, or of selecting a given number of objects, without counting them and without making a mistake. However, such gestures appear to our mind to be composed of a multitude of elements. They require the harmonious functioning of muscular and tactile senses, of the retina, of the eye and hand muscles, of innumerable nervous and muscular cells. Their simplicity is probably real, their complexity, artificial — that is, created by our techniques of observation. No object seems to be simpler, more homogeneous, than the water of the ocean. But, if we could examine this water through a microscope having a magnifying power of about one million diameters, its simplicity would vanish. The clear drop would become a heterogeneous population of molecules of different dimensions and shapes, moving at various speeds in an inextricable chaos. Thus, the
things of our world are simple or complex, according to the techniques that we select for studying them. In fact, functional simplicity always corresponds to a complex substratum. This is a primary datum of observation, which must be accepted just as it is.
Our tissues are of great structural heterogeneity. They are composed of many disparate elements. Liver, spleen, heart, kidneys are societies of specific cells. They are individuals definitely limited in space. For anatomists and surgeons, the organic heterogeneity of the body is unquestionable. Nevertheless, it may be more apparent than real. Functions are much less precisely located than organs. The skeleton, for example, is not merely the framework of the body. It also constitutes a part of the circulatory, respiratory, and nutritive systems, since, with the aid of the bone marrow, it manufactures leucocytes and red cells. The liver secretes, bile, destroys poisons and microbes, stores glycogen, regulates sugar metabolism in the entire organism, and produces heparin. In a like manner, the pancreas, the suprarenals, the spleen etc., do not confine themselves to one function. Each viscus possesses multiple activities and takes part in almost all the events of the body. Its structural frontiers are narrower than its functional ones. Its physiological individuality is far more comprehensive than its anatomical individuality. A cell community, by means of its manufactured products, penetrates all other communities. The vast cellular associations called viscera are placed, as we know, under the command of a single nervous centre. This centre sends its silent orders to every region of the organic world. In this way, heart, blood vessels, lungs, digestive apparatus, and endocrine glands become a functional whole in which all organic individualities blend.
Mode of organization of the body. Mechanical analogy. Antitheses and illusions
Indeed, both a machine and our body are organisms. But the organization of our body is not similar to that of the machine. A machine is composed of many parts, originally separate. Once these parts are put together, its manifoldness becomes unity. Like the human individual, it is assembled for a specific purpose. Like him, it is both simple and complex. But it is primarily complex and secondarily simple. On the contrary, man is primarily simple and secondarily complex. He originates from a single cell. This cell divides into two others, which divide
in their turn, and such division continues indefinitely. In the course of this process of structural elaboration, the embryo retains the functional simplicity of the egg. The cells seem to remember their original unity, even when they have become the elements of an innumerable multitude. They know spontaneously the functions attributed to them in the organized whole. If we cultivate epithelial cells over a period of several months, quite apart from the animal to which they belong, they arrange themselves in a mosaic, exactly as if to protect a surface. Yet the surface. to be protected is lacking. Leucocytes, living in flasks, industriously devour microbes and red corpuscles, although there is no organ ism to be defended against the incursions of these enemies. The innate knowledge of the part they must play in the whole is a mode of being of all the elements of the body....
An organ builds itself by techniques very foreign to the human mind. It is not made of extraneous material, like a house. Neither is it a cellular construction, a mere assemblage of cells. It is, of course, composed of cells, as a house is of bricks. But it is born from a cell, as if the house originated from one brick, a magic brick that would set about manufacturing other bricks. Those bricks, without waiting for the architect's drawings or the coming of the bricklayers, would assemble themselves and form the walls. They would also metamorphose into windowpanes, roofing-slates, coal for heating, and water for the kitchen and the bathroom. An organ develops by means such as those attributed to fairies in the tales told to children in bygone times. It is engendered by cells which, to all appearances, have a knowledge of the future edifice, and synthesize from substances contained in blood plasma the building material and even the workers.
These methods used by the organism do not have the simplicity of ours. They appear strange to us. Our intelligence does not encounter itself in the intraorganic world. It is modelled on the simplicity of the cosmic universe, and not on the complexity of the inner mechanisms of living beings. For the moment, we cannot understand the mode of organization of our body and its nutritive, nervous, and mental activities. The laws of mechanics, physics, and chemistry are completely applicable to inert matter. Partly, to man. The illusions of the mechanicists of the nineteenth century, the childish physicochemical conceptions of the human beings, in which so many physiologists and physicians still believe, have to be definitely abandoned.... Our knowledge
of the human body is, in truth, most rudimentary. It is impossible, for the present, to grasp its constitution. We must, then, be content with the scientific observation of our organic and mental activities. And, with out any other guide, march forward into the unknown.
Fragility and robustness of the body. Silence of the body during health
Our body is extremely robust. It adapts itself to all climates, arctic cold as well as tropical heat. It also resists starvation, weather inclemencies, fatigue, hardships, overwork. Man is the hardiest of all animals.... However, our organs are fragile. They are damaged by the slightest shock. They disintegrate as soon as blood circulation stops. Such contrast between the strength and the fragility of the organism is, like most of the antitheses encountered in biology, an illusion of our mind. We always unconsciously compare our body with a machine. The strength of a machine depends on the metal used in its construction, and on the perfection of the assembling of its parts. But that of man is due to other causes. His endurance comes more especially from the elasticity of his tissues, their tenacity, their property of growing instead of wearing out, from the strange power displayed by the organism in meeting a new situation by adaptive changes. Resistance to disease, work, and worries, capacity for effort, and nervous equilibrium are the signs of the superiority of a man....
The sound body lives in silence. We do not hear, we do not feel, its working. The rhythms of our existence are expressed by cenesthesic impressions which, like the soft whirring of a sixteen-cylinder motor, fill the depths of our consciousness when we are in silence and meditation. The harmony of organic functions gives a feeling of peace. When an organ begins to deteriorate, this peace may be disturbed. Pain is a signal of distress. Many people, although they are not ill, are not in good health. Perhaps the quality of some of their tissues is defective. The secretions of such gland, or such mucosa, may be insufficient or too abundant. The excitability of their nervous, system, exaggerated. Their organic functions, not exactly correlated in space or in time. Or their tissues, not as capable of resisting infections as they should be. Such individuals feel profoundly these organic deficiencies, which bring them much misery. The future discoverer of a method for inducing tissues and organs to develop harmoniously will be a greater
benefactor of humanity than Pasteur himself. For he will present man with the most precious of all gifts, with an almost divine offering, the aptitude for happiness.
From Alexis Carrel, Man the Unknown,
Wilco Publishing House, Bombay, 1959