What Is Physiology ? Alexis Carrel, who was French by birth, American by adoption, wrote Man, the Unknown in both French and English, writing parts in one language, parts in the other, then translating. After graduating in medicine from the University of Lyons, he spent two years in French hospitals, and a year each on the staffs at McMillan University in Montreal and at the University of Chicago. From 1906 until 1939, when he reached the retirement age of sixty- five, he worked at the Rockefeller Institute in New York, where he gained a world-wide reputation for his biological research.
During the First World War Dr. Carrel evolved a revolutionary method of treating deep injuries, rendering them aseptic by using a specially designed apparatus for pumping Darin’s solution into all parts of the wound. As far back as 1911 he had perfected a surgical technique that simplified blood transfusion.
In 1912 he won the Nobel Prize for success in suturing blood vessels and the transplantation of organs; in 1931 he was awarded the Hoffman-Jung medal for cancer research. Perhaps his most famous experiment was that in which for more than a quarter of a century he kept a section of chicken heart alive and growing by artificial feeding and elimination of waste. In Man, the Unknown Dr. Carrel has attacked the enigma at the very core of our existence—the secret of life itself.
Each man is characterised by his figure, his carriage, his face. The outward form expresses the qualities, the powers, of the body and mind. The man of the Renaissance, who was exposed continuously to dangers and inclemency, who was capable of as great an enthusiasm for the discoveries of Galileo as for the master- pieces of Leonardo avoidance, did not resemble modern man, lives in a steam-heated apartment, an air-conditioned office, who contemplates absurd films and plays golf and bridge.
Each epoch puts its seal on human beings. We begin to observe the new types created by motor-cars and athletics. Our form is moulded by our physiological habits, and even by our usual thoughts. The shape and lines of the face and mouth are determined by the habitual condition of the muscles. And the state of these muscles depends on that of the mind.
Unwittingly, the visage becomes more and more pregnant with the feelings, the appetites and the aspirations of the whole being; in this open book one can read not only the vices, the virtues, the intelligence, the stupidity, the most carefully concealed habits of an individual, but also the constitution of his body, and his tendencies to organic and mental diseases. 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.
Nutrition of tissues
The aspect of bones, muscles, skin and hair depends on the nutrition of tissues. And the nutrition of the tissues is regulated by the composition of blood plasma; that is, by the activity of the glandular and digestive systems. The surface of the skin reflects the conditions of the endocrine glands, the stomach, the intestines and the nervous system.
There are great functional disparities between tall and spare men and broad and short ones. The tall type is predisposed to tuberculosis and dementia praetor. The short, to cyclic mania, diabetes and rheumatism. In the diagnosis of diseases, ancient physicians quite rightly attributed great importance to temperament and idiosyncrasies. Each man bears on his face the description of his body and his soul.
The skin is the almost perfectly fortified frontier of a closed world. It is capable of destroying microbes living on its surface with the aid of substances secreted by its glands, and it is impermeable to water and gasses. 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.
Its durability is due 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.
Tactile corpuscles scattered all over the skin are sensitive to pressure, to pain, to heat or to cold. Those situated in the tongue are affected by certain qualities of food and also by temperature. Air vibrations act on the complex apparatus of the ear. The network of olfactory nerves is sensitive to odours. Thus the quality of an individual partly depends on that of his surface.
For the brain is moulded by the continual messages it receives from the outer world. Therefore the state of our envelope should not be modified thoughtlessly by new habits of life. For instance, we are far from knowing completely what effect exposure to sun-rays has upon the development of the entire body. Exaggerated tanning of the skin, therefore, should not be blindly accepted.
Living being when dead
One cannot understand the living being by studying the dead. 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 everywhere, bathing all tissues in lymph.
In order to apprehend this inner world as it is, we must study organs of living animals and of men as they are seen in surgical operations, and not simply those of cadavers. We must not separate cells from media, as anatomy has done. 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.
The blood is composed of about twenty-five or thirty thousand million red cells, and of fifty thousand million white cells. These cells are suspended in a liquid, the plasma. Blood carries to each tissue the proper nourishment, but acts, at the same time, as a 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 on its banks.
Blood plasma, incomparably richer than generally believed, contains proteins, acids, sugars, fats and the secretions of all glands and tissues. The nature of the majority of these substances and the immense complexity of their functions are very imperfectly known.
The blood also contains antibodies, which appear when the tissues have to defend themselves against invading microbes. In addition there is in blood plasma a protein, fibrin, which is changed into fibrin when a wound occurs-shreds of this fibrin adhere to wounds and stop haemorrhages.
The entire body is traversed by this stream of nutritive substances. The digestive membranes, with extraordinarily vast surfaces, are not only a filter, but also a chemical factory. The mucous membranes covering our inner surfaces secrete and absorb large quantities of fluids. Their cells allow the foodstuffs, when digested, to enter the body. But they resist the penetration of the bacteria that swarm in the digestive tract.
These dangerous enemies are always a menace. Viruses thrive in the pharynx and the nose, streptococci and microbes of diphtheria in the tonsils. The bacilli of typhoid fever and of dysentery multiply with ease in the intestines.
The soundness of the respiratory and digestive membranes governs, in a large measure, the resistance of the organism to infectious diseases, its equilibrium, its effective, its intellectual attitude.
The sexual glands intensify all physiological, mental and spiritual activities. No eunuch has ever become a great philosopher, a great scientist or even a great criminal. Testicles and ovaries secrete into the blood certain substances which give to all our functions their character.
The testicle engenders audacity, violence and brutality, the qualities distinguishing the fighting bull from the ox drawing the plough along the furrow. The ovary affects the organism of the woman in an analogous manner.
A fragment of living tissue, in a flask, must be given a volume of liquid equal to 2000 times its own volume, in order not to be poisoned within a few days by its waste products. Consequently, a human body reduced to pulp and artificially 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 quarts of fluid, instead of 200,000.The speed of circulation is sufficiently great to prevent the composition of blood from being modified by waste products.
Each organ regulates the volume and the rapidity of its blood flow by means of vasomotor nerves. Brain and other organs demand a certain tension of the blood. Our conduct depends, in large measure, on the state of our circulatory apparatus. All human activities are regulated by the condition of the nutritive medium.
When blood returns from the muscles and the organs, the pulsation of the heart drive it into the immense network of the lung capillaries, where each red corpuscle takes up atmospheric oxygen.
Simultaneously, carbon dioxide is expelled into the outside atmosphere by the respiratory movements. The purification of the blood is completed in the kidneys, which separate from the blood certain substances that are then eliminated from the body in the urine. They also regulate the quantity of salts indispensable to plasma.
The functioning of the kidneys and of the lungs is of a prodigious efficiency. It is their intense activity that permits the fluid medium required by living tissues to be so limited, and the human body to possess such compactness and agility.
Another kind of nutritive substance contained in blood, in addition to atmospheric oxygen and to products of intestinal digestion, consists of the secretions of the endocrine glands, which have the peculiar quality of manufacturing new compounds from the chemical substances of the blood.
These compounds serve to feed certain tissues and to stimulate certain functions. This sort of creation of itself by itself is analogous to the training of the will by an effort of the will.
Glands, such as the thyroid, the supra renal (or adrenal), the pancreas, synthesizer new compounds-thyroid, adrenaline and insulin. They are true chemical transformers. In this way, sub- stances indispensable for the nutrition of cells and organs, and for physiological and mental activities, are produced.
Such a phenomenon is as strange as if certain parts of a motor should create the oil used by other parts of the machine, the substances accelerating the combustion of the fuel, and even the thoughts of the engineer. To these glands is due the existence of the body with its manifold activities.
Man is, first of all, a nutritive process. He consists of a ceaseless motion of chemical substances. Matter perpetually flows through all the cells of the body, yielding to tissues the energy they need, and also the chemicals which build the temporary and fragile structure of our organs and humidors.
Functions of the body 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 leukocytes (white cells) and red cells.
The liver secretes bile, destroys poisons and microbes, stores glycogen and regulates sugar metabolism in the entire organism. In a like manner, the pancreas, the supernatural and the spleen do not confine themselves to one function. Each possesses multiple activities and takes part in almost all the events of the body
An organ is not limited by its surface. It reaches as far as the substance it secretes. Each gland extends, by means of its secretions, over the whole organism. Suppose the substances set free in the blood by testicles to be blue.
The entire body of the male would be blue. The testicles themselves would be more intensely coloured. But their specific hue would be diffused in all tissues and organs, even in the cartilages of the bones.
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 window-panes, roofing- slates, coal for heating and water for the kitchen and bathroom. An organ develops by means such as those attributed to fairies in the tales told to children. 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.
The body is extremely robust. It adapts itself to all climates- arctic cold as well as tropical heat. It also resists starvation, weather inclemency, fatigue, hardships. Man is the hardiest of all animals.
Body as a machine
We always unconsciously compare the body with a machine. The strength of a machine depends on the metal used in it. But the endurance of man comes from the elasticity of the tissues, their tenacity, their property of growing instead of wearing out; from their strange power of adaptive change. Resistance to disease, work and worries, capacity for effort, and nervous equilibrium are the signs of the superiority of a man.
Many people, although not ill, are not in good health. Perhaps the quality of some of their tissues is defective: the secretions of a gland or a mucous membrane may be insufficient or too abundant; the excitability of their nervous system exaggerated; or their tissues not as capable of resisting infections as they should be.
These deficiencies bring these individuals 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.
In illness the body preserves the same unity as in health. It is sick as a whole. No disturbance remains strictly confined to a single organ. Doctors have been led to consider each disease as a speciality by the old anatomical conception of the human being. Only those physicians who know man both in his parts and in his entirety, physically and mentally, are capable of understanding him when he is sick.
The cerebral centres consist partly of fluids containing the gland and tissue secretions that diffuse through the entire body. Thus every organ is present in the cerebral cortex. When blood and lymph are deprived of the secretions of the supra renal glands, the patient falls into a depression.
Everyone knows how human personality is modified by diseases of the liver, the stomach and the intestines. Obviously, the cells of the organs discharge into the bodily fluids certain substances that react upon our mental and spiritual functions.
The testicle exerts a profound influence upon the strength and quality of the mind. In general, great poets, artists and saints, as well as conquerors, are strongly sexed. The removal of the genital glands produces some modifications of the mental state. Inspiration seems to depend on a certain condition of the sexual glands. Love stimulates the mind when it does not attain its object.
If Beatrice had been the mistress of Dante, there would perhaps be no Divine Comedy. It is well known that sexual excesses impede in intellectual activity. In order to reach its full power, intelligence seems to require both the presence of well-developed sexual glands and the temporary repression of the sexual appetite.
Envy, hate, fear, when these sentiments are habitual, are capable of starting organic changes and genuine diseases. Moral suffering profoundly disturbs health. Businessmen who do not know how to fight worry die young. Emotions affect the dilatation or the contraction of the small arteries, through the vasomotor nerves. They are, therefore, accompanied by changes in blood circulation. Pleasure causes the skin of the face to flush. Fear turns it white.
The affective states stimulate or stop the gland secretions, or modify their chemical constitution. It has been proved that a moral shock may cause marked changes in the blood. Thought can generate organic lesions.
The instability of modern life, the ceaseless agitation, create states of consciousness which bring about nervous and organic disorders of the stomach and of the intestines, defective nutrition and passage of intestinal microbes into the circulatory apparatus. Such diseases are almost unknown in social groups where life is simpler, where anxiety is less constant.
Likewise, those who keep the peace of their inner self in the midst of tumult are immune from nervous and organic disorders. Man thinks, invents, loves, suffers, admires and prays with his brain and all his organs.
Mental activities improve with exercise. Intelligence has to be moulded by the habit of logical thinking. Every human being is born with different intellectual capacities. But, great or small, these potentialities require constant exercise.
Intellectual power is augmented by the habit of precise reasoning, the study of logic, mental discipline and deep observation of things. On the contrary, superficial observations, a rapid succession of impressions and lack of intellectual discipline hinder the development of the mind.
In order to reach its highest development the mind probably demands an ensemble of conditions, which has occurred only at certain epochs. What were the modes of existence, the diet and the education of the men of the great periods of the history of civilisation We are almost totally ignorant of the genesis of intelligence.
And we believe that the minds of children can be developed by the mere training of their memory and by exercises practised in modern schools! 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 to disintegration in a few hours. He accommodates himself, much better than animals do, to changing conditions, to physical, economic and social upheavals. Instead of wearing out, the body changes. Our organs improvise means of meeting every new situation.
When one half of the thyroid gland is removed, the remaining half increases in volume, generally increasing more than is necessary. 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 the secretion of a gland is insufficient, other glands augment their activity to supplement its work.
Each element of the body adjusts itself to the others, and the others to it through a correlation of the organic fluids and the nervous system. Each part seems to know the present and future needs of the whole, and acts accordingly. The body perceives the remote 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, rendering 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.
During the entire history of the embryo the tissues prepare for the future. The component parts of the eye, for example, associate for a definite, although future, purpose. The brain causes a part of itself, the optic nerve and the retina, to shoot out towards the surface. The skin overlying the young retina undergoes an astonishing modification.
It becomes transparent, forms the cornea and the crystalline lens, building up the prodigious optical system which we call the eye. 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. In addition, the form of the lens automatically adjusts itself to near or distant vision. These correlations cannot be explained.
The correlation of organic processes is evident after a haemorrhage. First, all the vessels contract. The relative volume of the remaining blood automatically increases. The heart beats faster. Thus arterial pressure is sufficiently restored for blood circulation to continue. The fluids of the tissues 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 re- serves 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 to the phenomena.
When skin, muscles, blood vessels or bones are injured, the organism immediately adapts itself. Everything happens as if a series of measures were taken by the body in order to repair the damage. As in blood regeneration, converging mechanisms come into play.
An artery is cut. Blood gushes in abundance. Arterial pressure is lowered. The patient feels a sudden faintness. The haemorrhage decreases. A clot of fibrin forms in the wound. Then the haemorrhage stops. During the following days, leukocytes and tissue cells invade the clot and progressively regenerate the wall of the artery.
When a limb is broken, sharp ends of the fractured bones may tear muscles and blood vessels. They are soon surrounded by a blood clot. Then, circulation becomes more active. The limb swells. The nutritive substances necessary for the regeneration of the tissues are brought into the wounded area. All processes are directed towards repair.
During the period of repair, an immense number of chemical, nervous, circulatory and structural phenomena take place. They are all linked together. The blood flowing from the vessels at the time of the accident sets in motion the physio- logical processes of regeneration. Each phenomenon results from the preceding one.
Knowledge of these healing processes has brought about modern surgery. 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.
It seems that the work of the adaptive mechanisms stimulates all organic functions. Man attains his highest development when he is exposed to the rigors of the seasons, when his meals are sometimes abundant and sometimes scanty, when he conquers food and shelter by strenuous effort.
He has also to train his muscles, to tire himself and rest, to fight, to suffer and to be happy, to love and to hate. His will alternately needs 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 digest- ing food.
When his adaptive processes work most intensely, he develops his virility to the fullest extent. 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. 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 a heater in 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 hours against snow, rain or sun. In former times the mechanisms responsible for regulating the temperature of blood and humours were maintained in constant activity by the struggle against the rigours of the weather. Today they are in a state of perpetual rest.
Rougher conditions of existence and more responsibility would restore man’s moral energy and audacity. More virile habits should be substituted for the uniformity and softness of life in schools. The adaptation of the individual to discipline determines definite changes in the nervous system, the endocrine glands and the mind. The organism thus acquires a better integration, and greater vigour to overcome the difficulties of existence.
Man naturally tends towards the satisfaction of his appetites, such as the cravings for alcohol, speed and ceaseless change. But he degenerates when he satisfies these appetites completely. He must accustom himself to dominating his hunger, his sexual impulses, his laziness, his fondness for alcohol, his need for sleep.
Modern man sleeps too much or not enough. He does not easily adapt himself in this respect. It is useful to accustom one- self 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 modern habits. The individual and the race are weakened by extreme poverty. Wealth is just as dangerous. In the poor, as well as in the rich, leisure engenders degeneration. Cinemas, concerts, motor-cars and athletics are no substitute for intelligent work.
Two essential conditions for the progress of the individual are relative isolation and discipline. Every individual can submit himself to these conditions. One has the power of refusing to go to certain cinemas, to listen to music and entertainment programmes, to read certain newspapers or books. But it is chiefly through intellectual and moral discipline, and the rejection of the habits of the herd, that we can reconstruct ourselves.
Such discipline is particularly essential in middle and old age. Senescence seems to be delayed when the body and mind are kept working. Work is more effective than alcohol and morphine in helping to bear adverse conditions. Inaction augments all sufferings. Man is indelibly marked by prolonged and intense mental effort.
All physiological and mental functions are improved by work. The more the muscle works, the more it develops. Activity strengthens it, instead of wearing it out. An organ atrophies when not used. Like muscles and organs, intelligence and moral sense atrophy for want of exercise. Effort is indispensable to the optimum development of the individual.
‘Man, the Unknown’ is published by Hamish Hamilton, London
What is physiology
Man, the Unknown
Condensed from the book by
DR. ALEXIS CARREL