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Chapter V
INWARD TIME
THE DURATION of man, just as his size, varies according to the unit used for its measurement. It is long when related to that of mice or butterflies. Short in comparison with the life of an oak. Insignificant, if placed in the frame of the earth's history. We measure it by the motion of the hands of a clock around the dial. We liken it to the passage of those hands over equal intervals, the seconds, the minutes, the hours. The time of a clock corresponds to certain rhythmic events, such as the earth's rotation on its axis and around the sun. Our duration is, then, expressed in units of solar time and consists of about twenty-five thousand days. For the clock which measures it, a child's day is equal to that of its parents. In reality, those twenty-four hours represent a very small part of the child's future life, and a much larger fraction of that of its parents. But they may also be looked upon as a minute fragment of an old man's past existence and a far more important part of that of a nursling. Thus, the value of physical time seems to differ according to whether we look back to the past or forward to the future.
We have to refer our duration to a clock because we are immersed in the physical continuum. And the clock measures one of the dimensions of this continuum. On the surface of our planet, those dimensions are discerned through particular characteristics. The vertical is identified by the phenomenon of gravity. We are unable to make any distinction between the two horizontal dimensions. We could, however, separate them from each other if our nervous system were endowed with the properties of a magnetic needle. As for the fourth dimension, or time, it takes on a strange aspect. While the other three dimensions of things are short and almost motionless, it appears as ceaselessly extending and very long. We travel quite easily over the two horizontal dimensions. But in order to move in the vertical one, we must use a staircase or an elevator, an aircraft or a balloon, for we have to contend with gravity. To travel in time is absolutely impossible. Wells has not divulged the secrets of construction of the machine which enabled one of his heroes to leave his room by the fourth dimension and to escape into the future. For concrete man, time is very different from space. But the four dimensions would seem identical to an abstract man inhabiting the sidereal spaces. Although distinct from space, time is inseparable from it, at the surface of the earth as in the rest of the universe, when considered by the biologist as well as by the physicist.
In nature, time is always found united to space. It is a necessary aspect of material beings. No concrete thing has only three spatial dimensions. A rock, a tree, an animal cannot be instantaneous. Indeed, we are capable of building up in our minds beings entirely described within three dimensions. But all concrete objects have four. And man extends both in time and in space. To an observer living far more slowly than we do he would appear as something narrow and elongated, analogous to the incandescent trail of a meteor. Besides, he possesses another aspect, impossible to define clearly. For he is not wholly comprised within the physical continuum. Thought is not confined within time and space. Moral, esthetic, and religious activities do not inhabit the physical continuum exclusively. Moreover, we know that clairvoyants may detect hidden things at great distances. Some of them perceive events which have already happened or which will take place in the future. It should be noted that they apprehend the future in the same way as the past. They are sometimes incapable of distinguishing the one from the other. For example, they may speak, at two different epochs, of the same fact, without suspecting that the first vision relates to the future, and the second to the past. Certain activities of consciousness seem to travel over space and time.
The nature of time varies according to the objects considered by our mind. The time that we observe in nature has no separate existence. It is only a mode of being of concrete objects. We ourselves create mathematical time. It is a mental construct, an abstraction indispensable to the building up of science. We conveniently compare it to a straight line, each successive instant being represented by a point. Since Galileo's day this abstraction has been substituted for the concrete data resulting from the direct observation of things. The philosophers of the Middle Ages considered time as an agent concretizing abstractions. Such a conception resembled more closely that of Minkowski than that of Galileo. To them, as to Minkowski, to Einstein, and to modern physicists, time, in nature, appeared as completely inseparable from space. In reducing objects to their primary qualities--that is, to what can be measured and is susceptible of mathematical treatment --Galileo deprived them of their secondary qualities, and of duration. This arbitrary simplification made possible the development of physics. At the same time, it led to an unwarrantably schematic conception of the world, especially of the biological world. We must listen to Bergson and attribute to time a reality of its own. And give back their secondary qualities and duration to inanimate and living beings.
The concept of time is equivalent to the operation required to estimate duration in the objects of our universe. Duration consists of the superposition of the different aspects of an identity. It is a kind of intrinsic movement of things. The earth revolves on its axis and, without losing its primary qualities, shows a surface which is sometimes lighted and sometimes darkened. Mountains may progressively change their shape under the action of snow, rain, and erosion, although they remain themselves. A tree grows, and does not lose its identity. The human individual retains his personality throughout the flux of the organic and mental processes that make up his life. Each inanimate or living being comprises an inner motion, a succession of states, a rhythm, which is his very own. Such motion is inherent time. It can be measured by reference to the motion of another being. Thus, we measure our duration by comparing it with solar time. As we inhabit the surface of the earth, we find it convenient to place in its frame the spatial and temporal dimensions of everything found thereon. We estimate our height with the aid of the meter, which is approximately the forty-millionth part of the meridian of our planet. In a like manner, the rotation of the earth, or the number of hours ticked off by a clock, is the standard to which we refer our temporal dimensions or the flow of our time. It is natural for human beings to use the intervals separating the rising of the sun from its setting as the means to measure their duration and organize their lives. However, the moon could serve the same purpose. In fact, to fishermen dwelling on shores where the tides are very high, lunar time is more important than solar time. Their way of living, and the hours reserved for sleeping and eating, are determined by the rhythm of the tides. In such circumstances, human duration is fitted into the frame of the daily variations of the sea-level. In short, time is a specific character of things. Its nature varies according to the constitution of each object. Human beings have acquired the habit of identifying their duration, and that of all other beings, with the time shown by clocks. Nevertheless, our inner time is as distinct from, and independent of, this extrinsic time, as our body is, in space, distinct from, and independent of, the earth and the sun.
Inner time is the expression of the changes of the body and its activities during the course of life. It is equivalent to the uninterrupted succession of the structural, humoral, physiological, and mental states which constitute our personality. It is truly a dimension of ourselves. Imaginary slices carved from our body and soul through such dimension would be as heterogeneous as the sections made by anatomists perpendicularly to the three spatial axes. As Wells says in the Time Traveller, a man's portraits at eight years, fifteen years, seventeen years, twenty-three years, and so on, are sections, or rather images, in three dimensions of a being of four dimensions who is a fixed and unalterable thing. The differences between these sections express changes progressively occurring in the constitution of the individual. These changes are organic and mental. Thus, inward time has to be divided into physiological and psychological times.
Physiological time is a fixed dimension, consisting of the series of all organic changes undergone by a human being from the beginning of his embryonic life to his death. It may also be considered as a movement, as the successive states which build up our fourth dimension under the eyes of the observer. Some of these states are rhythmic and reversible, such as the pulsations of the heart, the contractions of the muscles, the movements of the stomach and those of the intestines, the secretions of the glands of the digestive apparatus, and the phenomena of menstruation. Others are progressive and irreversible, such as the loss of the skin's elasticity, the increase in the quantity of the red blood cells, the sclerosis of the tissues and the arteries. But the rhythmic and reversible movements are likewise altered during the course of life. They themselves also undergo a progressive and irreversible change. Simultaneously, the constitution of the tissues and the humors becomes modified. This complex movement is physiological time.
The other aspect of inner time is psychological time. Consciousness, under the influence of the stimuli coming from the outside world, records its own motion, the series of its states. Time, according to Bergson, is the very stuff of psychological life. "Duration is not one instant replacing another. . . . Duration is the continuous progress of the past which gnaws into the future and which swells as it advances. . . . The piling up of the past upon the past goes on without relaxation. In reality, the past is preserved by itself, automatically. In its entirety, probably, it follows us at every instant. . . . Doubtless we think with only a small part of our past, but it is with our entire past, including the original bent of our soul, that we desire, will and act."1 We are a history. And the length of that history, rather than the number of our years, expresses the wealth of our inner life. We obscurely feel that we are not today identical with what we were yesterday. The days seem to fly more and more rapidly. But none of these changes is sufficiently precise or constant to be measured. The intrinsic motion of our consciousness is indefinable. Certain of our psychological activities are not modified by duration. They deteriorate only when the brain succumbs to illness or to senility.
1 Bergson, Henri. Creative Evolution, 4-5. Translation by Arthur Mitchell. New York, Henry Holt and Company, Inc.
Inward time cannot be properly measured in units of solar time. However, it is generally expressed in days and years because these units are convenient and applicable to the classification of terrestrial events. But such a procedure gives no information about the rhythm of the inner processes constituting our intrinsic time. Obviously, chronological age does not correspond to physiological age. Puberty occurs at different epochs in different individuals. It is the same with menopause. True age is an organic and functional state. It has to be measured by the rhythm of the changes of this state. Such rhythm varies according to individuals. Some remain young for many years. On the contrary, the organs of others wear out early in life. The value of physical time in a Norwegian, whose life is long, is far from being identical with that in an Eskimo, whose life is short. To estimate true, or physiological, age, we must discover, either in the tissues or in the humors, a measurable phenomenon, which progresses without interruption during the whole lifetime.
Man is constituted, in his fourth dimension, by a series of forms following, and blending into, each other. He is egg, embryo, infant, adolescent, adult, mature and old man. These morphological aspects are the expression of chemical, organic, and psychological events. Most of these variations cannot be measured. When measurable, they are generally found to take place only during a certain period of the existence of the individual. But physiological duration is equivalent to our fourth dimension in its entire length. The progressive slackening of growth during infancy and youth, the phenomena of puberty and of menopause, the diminution of basal metabolism, the whitening of the hair, etc., are the manifestations of different stages of our duration. The rate at which tissues grow also declines with age. Such growth activity may be roughly estimated in fragments of tissues extirpated from the body and cultivated in flasks. But, as far as the age of the organism itself is concerned, the information thus obtained is far from being reliable. Indeed, some tissues grow more active, others less active, at certain periods of physiological life. Each organ changes at its own rhythm, which differs from that of the body as a whole. Certain phenomena, however, express a general modification of the organism. For example, the rate of healing of a superficial wound varies in function of the age of the patient. It is well known that the progress of cicatrization can be calculated with two equations set up by Lecomte du Noüy. The first of these equations gives a coefficient, called index of cicatrization, which depends on the surface and the age of the wound. By introducing this index in a second equation, one may, from two measurements of the wound taken at an interval of several days, predict the future progress of repair. The smaller the wound and the younger the man, the greater is the index. With the help of this index, Lecomte du Noüy has discovered a constant that expresses the regenerative activity characteristic of a given age. This constant is equal to the product of the index by the square root of the surface of the wound. The curve of its variations shows that a twenty-year-old patient heals twice as quickly as a forty-year-old one. Through these equations, the physiological age of a man can be deduced from the rate of healing of a wound. From ten to about forty-five years, the information thus obtained is very definite. But later, the variations of the index of cicatrization are so small that they lose all significance.
Blood plasma alone displays, throughout the entire lifetime, progressive modifications characterizing the senescence of the body as a whole. We know that it contains the secretions of all tissues and organs. Plasma and tissues being a closed system, any alteration in the tissues reacts on the plasma, and vice versa. During the course of life, this system undergoes continuous changes. Some of these changes may be detected both by chemical analysis and by physiological reactions. The plasma or the serum of an aging animal has been found to increase its restraining effect on the growth of cell colonies. The ratio of the area of a colony living in serum, to that of an identical colony living in a saline solution and acting as a control, is called the growth index. The older the animal to which the serum belongs, the smaller is this index. Thus, the rhythm of physiological time can be measured. During the first days of life, blood serum does not inhibit the growth of cell colonies any more than does the control solution. At this moment the value of the index approaches unity. As the animal becomes older, its serum restrains cell multiplication more effectively. And the index decreases. During the last years of life, it is generally equal to zero.
Although very imperfect, this method gives some precise information on the rhythm of physiological time at the beginning of life, when aging is rapid. But in the final period of maturity, when aging is slow, it becomes quite insufficient. By the variations of the growth index the life of a dog can be divided into ten units of physiological time. The duration of this animal may roughly be expressed in these units instead of in years. Thus, it has become possible to compare physiological time with solar time. And their rhythms appear to be very different. The curve showing the decrease of the index value in function of chronological age falls sharply during the first year. During the second and third years, its slope becomes less and less pronounced. The segment of the curve corresponding to the mature years has a tendency to become a straight line. And the portion representing old age does not deviate from the horizontal. Obviously, aging progresses much more rapidly at the beginning than at the end of life. When infancy and old age are expressed in solar years, infancy appears to be very short and old age very long. On the contrary, measured in units of physiological time, infancy is very long and old age very short.
We have mentioned that physiological time is quite different from physical time. If all the clocks accelerated or retarded their motion, and if the earth correspondingly modified the rhythm of its rotation, our duration would remain unchanged. But it would seem to decrease or to increase. In this manner, the alteration undergone by solar time would become apparent. While we are swept onward upon the stream of physical time, we move at the rhythm of the inner processes constituting physiological duration. Indeed, we are not mere grains of dust floating on a river. But also drops of oil spreading out over the surface of the water with a motion of their own, while being borne along by the current. Physical time is foreign to us, whereas inner time is ourself. Our present does not drop into nothingness as does the present of a pendulum. It is recorded simultaneously in mind, tissues, and blood. We keep within ourselves the organic, humoral, and psychological marks of all the events of our life. Like a nation, like an old country, like the cities, the factories, the farms, the cultivated fields, the Gothic cathedrals, "the feudal castles, the Roman monuments of Europe, we are the result of a history. Our personality is enriched by each new experience of our organs, humors, and consciousness. Each thought, each action, each illness, has definitive consequences, inasmuch as we never separate ourselves from our past. We may completely recover from a disease, or from a wrong deed. But we bear forever the scar of those events.
Solar time flows at a uniform rate. It consists of equal intervals. Its pace never changes. On the contrary, physiological time differs from one man to another. In the races enjoying long life, it is slower, and more rapid in those whose life is short. It also varies within a single individual at the different periods of his life. A year is richer in physiological and mental events during infancy than during old age. The rhythm of these events decreases rapidly at first, and later on much more slowly. The number of units of physical time corresponding to a unit of physiological time becomes progressively greater. In short, the body is an ensemble of organic movements, whose rhythm is very fast during infancy, much less rapid during youth, and very slow in maturity and old age. It is when our physiological activities begin to weaken that our mind attains the summit of its development.
Physiological time is far from having the precision of a clock. Organic processes undergo certain fluctuations. Their rhythm is not constant. Their slackening in the course of life is expressed by an irregular curve. These irregularities are due to accidents in the concatenation of the physiological phenomena constituting our duration. At some moments, the progress of age seems to cease. At other periods, it accelerates. There are also phases in which personality concentrates and grows, and phases in which it dissipates. As stated above, inner time and its organic and psychological substratum do not possess the regularity of solar time. A sort of rejuvenation may be brought about by a happy event, or a better equilibrium of the physiological and psychological functions. Possibly, certain states of mental and bodily well-being are accompanied by modifications of the humors characteristic of a true rejuvenation. Moral suffering, business worries, infectious and degenerative diseases accelerate organic decay. The appearance of senescence may be induced in a dog by injections of sterile pus. The animal grows thin, becomes tired and depressed. At the same time, his blood and tissues display physiological reactions analogous to those of old age. But those reactions are reversible and, later, the organic functions reestablish their normal rhythm. An old man's aspect changes but slightly from one year to another. In the absence of disease, senescence is a very slow process. When it becomes rapid, the intervention of factors other than physiological ones are to be suspected. In general, such a phenomenon may be accounted for by anxiety and sorrow, by substances deriving from bacterial infections, by a degenerating organ, or by cancer. The speeding up of senescence always expresses the presence of an organic or moral lesion in the aging body.
Like physical time, physiological time is irreversible. In fact, it is as irreversible as the processes responsible for its existence. In the higher animals, duration never changes its direction. However, in hibernating mammals, it becomes partly suspended. In a dried rotifer, its flow comes to a complete standstill. The organic rhythm of cold-blooded animals accelerates when their environment becomes warmer. The flies kept by Jacques Loeb at an abnormally high temperature aged much more rapidly and died sooner. Likewise, the value of the physiological time of an alligator changes if the surrounding temperature goes up from 20° to 40° C. In this instance, the index of cicatrization of a superficial wound rises and falls with the temperature. But, in using such simple procedures, it is not possible to induce in men any profound change of the tissues. The rhythm of physiological time is not modifiable except by interference with certain fundamental processes and their mode of association. We cannot retard senescence, or reverse its direction, unless we know the nature of the mechanisms which are the substratum of duration.
Physiological duration owes its existence and its characteristics to a certain type of organization of animate matter. It appears as soon as a portion of space containing living cells becomes relatively isolated from the cosmic world. At all levels of organization, in the body of a cell or in that of a man, physiological time depends on modifications of the medium produced by nutrition, and on the response of the cells to those modifications. A cell colony begins to record time as soon as its waste products are allowed to stagnate, and thus to alter its surroundings. The simplest system, where the phenomenon of senescence is observed, consists of a group of tissue cells cultivated in a small volume of nutritive medium. In such a system, the medium is progressively modified by the products of nutrition and, in its turn, modifies the cells. Then appear senescence and death. The rhythm of physiological time depends on the relations between the tissues and their medium. It varies according to the volume, the metabolic activity, the nature of the cell colony, and the quantity and the chemical composition of the fluid and gaseous media. The technique used in the preparation of a culture accounts for the rhythm of life of such culture. For example, a fragment of heart fed with a single drop of plasma in the confined atmosphere of a hollow slide, and another one immersed in a flask containing a large volume of nutritive fluids and gases, have quite different fates. The rate of accumulation of the waste products in the medium, and the nature of these products, determine the characteristics of the duration of the tissues. When the composition of the medium is maintained constant, the cell colonies remain indefinitely in the same state of activity. They record time by quantitative, and not by qualitative, changes. If, by an appropriate technique, their volume is prevented from increasing, they never grow old. Colonies obtained from a heart fragment removed in January, 1912, from a chick embryo, are growing as actively today as twenty-three years ago. In fact, they are immortal.
Within the body, the relations of the tissues and of their medium are incomparably more complex than in the artificial system represented by a culture of cells. Although the lymph and the blood, which constitute the organic medium, are continually modified by the waste products of cell nutrition, their composition is maintained constant by the lungs, kidneys, liver, etc. However, in spite of these regulatory mechanisms, very slow changes do take place in humors and tissues. They are detected by variations in the growth index of plasma, and in the constant that expresses the regenerative activity of skin. They correspond to successive states in the chemical composition of the humors. The proteins of blood serum become more abundant and their characters are modified. It is chiefly the fats which give to serum the property of acting upon certain cell types and of diminishing the rapidity of their multiplication. These fats increase in quantity and change in nature during life. The modifications of serum are not the result of a progressive accumulation, of a sort of retention of fats and proteins in the organic medium. It is quite easy to remove from a dog the greater part of its blood, to separate the plasma from the corpuscles, and to replace it by a saline solution. The blood cells, thus freed from the proteins and fatty substances of plasma, are reinjected into the animal. In less than a fortnight, plasma is observed to be regenerated by the tissues, without any change in its composition. Its state is, therefore, due to the condition of the tissues, and not to an accumulation of harmful substances. And this state is specific of each age. Even if blood serum is removed several times, it always regenerates with the characteristics corresponding to the age of the animal. The state of the humors during senescence thus appears to be determined by substances contained in the organs as in almost inexhaustible reservoirs.
In the course of life, the tissues undergo important alterations. They lose much water. They are encumbered with nonliving elements and connective fibers, which are neither elastic nor extensible. The organs acquire more rigidity. Arteries become hard. Circulation is less active. Profound modifications take place in the structure of the glands. Epithelial cells lose their qualities little by little. They regenerate more slowly, or not at all. Their secretions are less rich. Such changes occur at various rates, according to the organs. Certain organs grow old more rapidly than others. But we do not know as yet the reason for this phenomenon. Such regional senescence may attack the arteries, the heart, the brain, the kidneys, or any other organ. The aging of a single system of tissues is dangerous. Longevity is much greater when the elements of the body grow old in a uniform way. If the skeletal muscles remain active when the heart and the vessels are already worn out, they become a danger to the entire body. Abnormally vigorous organs in a senile organism are almost as harmful as senile organs in a young organism. The youthful functioning of any anatomical system, either sexual glands, digestive apparatus, or muscles, is very dangerous for old men. Obviously, the value of time is not the same for all tissues. This heterochronism shortens the duration of life. If excessive work is imposed on any part of the body, even in individuals whose tissues are isochronic, aging is also accelerated. An organ which is submitted to overactivity, toxic influences, and abnormal stimulations, wears out more quickly than the others. And its premature senility brings on the death of the organism.
We know that physiological time, like physical time, is not an entity. Physical time depends on the constitution of the clocks and of the solar system. Physiological time, on that of tissues and humors, and on their reciprocal relations. The characteristics of duration are those of the structural and functional processes specific of a certain type of organization. The length of life is conditioned by the very mechanisms that make man independent of the cosmic environment and give him his spatial mobility. By the small volume of the blood. By the activity of the systems responsible for the purification of the humors. These systems do not succeed in preventing certain progressive modifications of the serum and the tissues from occurring. Perhaps the tissues are not completely freed of waste products by the blood stream. Perhaps they are insufficiently fed. If the volume of the organic medium were much greater, and the elimination of waste products more complete, human life might last longer. But our body would be far larger, softer, less compact. It would resemble the gigantic prehistoric animals. We certainly would be deprived of the agility, the speed, and the skill that we now possess.
Like physiological time, psychological time is only an aspect of ourselves. Its nature, as that of memory, is unknown. Memory is responsible for our awareness of the passage of time. However, psychological duration is composed of other elements. Personality is partly made up of recollections. But it also comes from the impression left upon all our organs by every physical, chemical, physiological, or psychological event of our life. We obscurely feel the passing of duration. We are capable of estimating such duration, in a grossly approximative manner, in terms of physical time. We perceive its flux as, perhaps, do muscular or nervous elements. Each cell type records physical time in its own way. The value of time for nerves and muscles is expressed, as already mentioned, in chronaxies. All anatomical elements are far from having the same chronaxy. The isochronism and heterochronism of cells play a capital part in their work. This estimation of time by the tissues may possibly reach the threshold of consciousness, and be responsible for the indefinable feeling in the depths of our self of silently flowing waters, on which float our states of consciousness, like the spots of a searchlight on the dark surface of an immense river. We realize that we change, that we are not identical with our former self. But that we are the same being. The distance from which we look back upon the small child, who was ourself, is precisely the dimension of our organism and of our consciousness which we compare to a spatial dimension. Of this aspect of inward time we know nothing, except that it is both dependent and independent of the rhythm of organic life, and moves more and more rapidly as we grow older.
The greatest desire of men is for eternal youth. From Merlin down to Cagliostro, Brown-Sequard, and Voronoff, charlatans and scientists have pursued the same dream and suffered the same defeat. No one has discovered the supreme secret. Meanwhile, our need of it is becoming more and more urgent. Scientific civilization has destroyed the world of the soul. But the realm of matter is widely opened to man. He must, then, keep intact the vigor of his body and of his intelligence. Only the strength of youth gives him the power to satisfy his physiological appetites and to conquer the outer world. In some measure, however, we have realized the ancestral dream. We enjoy youth, or its appearance, for a much longer time than our fathers did. But we have not succeeded in increasing the duration of our existence. A man of forty-five has no more chance of dying at the age of eighty years now than in the last century.
This failure of hygiene and medicine is a strange fact. In spite of the progress achieved in the heating, ventilation, and lighting of houses, of dietary hygiene, bathrooms, and sports, of periodical medical examinations, and increasing numbers of medical specialists, not even one day has been added to the span of human life. Are we to believe that hygienists, chemists, and physicians are mistaken in their ruling of the existence of the individual, like politicians, economists, and financiers in the organization of the life of the nation? After all, it may be that modern comfort and habits imposed upon the dwellers of the new city do not agree with natural laws. However, a marked change has taken place in the appearance of men and women. Owing to hygiene, athletics, alimentary restrictions, beauty parlors, and to the superficial activity engendered by telephone and automobile, all are more alert than in former times. At fifty, women are still young. Modern progress, however, has brought in its train counterfeit money as well as gold. When their visages, lifted and smoothed by the beauty surgeon, again become flabby, when massage no longer prevails against invading fat, those women whose appearance has been girlish for so many years look older than their grandmothers did at the same age. The pseudo-young men, who play tennis and dance as at twenty years, who discard their old wife and marry a young woman, are liable to softening of the brain, and to diseases of the heart and the kidneys, Sometimes they die suddenly in their bed, in their office, on the golf-links, at an age when their ancestors were still tilling their land or managing their business with a firm hand. The causes of this failure of modern life are not exactly known. Indeed, hygienists and physicians cannot be held responsible for it. The premature wearing out of modern men is probably due to worries, lack of economic security, overwork, absence of moral discipline, and excesses of all sorts.
A better knowledge of the mechanisms of physiological duration could bring a solution of the problem of longevity. But the science of man is still too rudimentary to be useful. We must, then, ascertain, in a purely empirical manner, whether life can be made longer. The presence of a few centenarians in every country demonstrates the extent of our temporal potentialities. No practical conclusions, however, have resulted so-far from the observation of these centenarians. Obviously, longevity is hereditary. But it depends also on the conditions of development. When descendants of families where longevity is usual come to dwell in large cities, they generally lose, in one or two generations, the capacity of living to be old. A study of animals of pure stock and of well-known ancestral constitution would probably show in what measure environment may augment the span of existence. In certain races of mice, mated between brothers and sisters over many generations, the duration of life remains quite constant. However, if one places the animals in large pens, in a state of semi-liberty, instead of keeping them in cages, and allows them to burrow and return to more primitive conditions of existence, they die much earlier. When certain substances are removed from the diet, longevity is also found to decrease. On the contrary, life lengthens if the animals are given certain food or subjected to fasting during certain fixed periods for several generations. It is evident that simple changes in the mode of existence are capable of influencing the duration of life. Man's longevity could probably be augmented by analogous, or other, procedures.
We must not yield to the temptation to use blindly for this purpose the means placed at our disposal by medicine. Longevity is only desirable if it increases the duration of youth, and not that of old age. The lengthening of the senescent period would be a calamity. The aging individual, when not capable of providing for himself, is an encumbrance to his family and to the community. If all men lived to be one hundred years old. the younger members of the population could not support such a heavy burden. Before attempting to prolong life, we must discover methods for conserving organic and mental activities to the eve of death. It is imperative that the number of the diseased, the paralyzed, the weak, and the insane should not be augmented. Besides, it would not be wise to give everybody a long existence. The danger of increasing the quantity of human beings without regard to their quality is well known. Why should more years be added to the life of persons who are unhappy, selfish, stupid, and useless? The number of centenarians must not be augmented until we can prevent intellectual and moral decay, and also the lingering diseases of old age.
It would be more useful to discover a method for rejuvenating individuals whose physiological and mental qualities justify such a measure. Rejuvenation can be conceived as a complete reversal of inward time. The subject would be carried back to a previous stage of his life by some operation. One would amputate a part of his fourth dimension. However, for practical purposes, rejuvenation should be given a more restricted meaning and be considered as an incomplete reversal of duration. The direction of psychological time would not be changed. Memory would persist. Tissues and humors would be rejuvenated. With the help of organs in possession of their youthful vigor, the subject could utilize the experience acquired in the course of a long life. The word rejuvenation, when used in connection with the experiments and operations carried out by Steinach, Voronoff, and others, refers to an improvement in the general condition of the patients, to a feeling of strength and of sprightliness, to a revival of the sexual functions. But such changes occurring in an old man after the treatment do not mean that rejuvenation has taken place. Studies of the chemical composition of the blood serum, and of its physiological reactions, are the only means of detecting a reversal of physiological age. A permanent increase in the growth index of serum would demonstrate the reality of results claimed by the surgeons. For rejuvenation is equivalent to certain physiological and chemical modifications measurable in blood plasma. Nevertheless, the absence of such findings does not necessarily mean that the age of the subject has not decreased. Our techniques are still far from perfect. They cannot reveal, in an old individual, a reversal of physiological time of less than several years. If a fourteen-year-old dog were brought back to the age of ten, the change in the growth index of his serum would be hardly discernible.
Among the ancient medical superstitions, there was a persistent belief in the virtue of young blood, in its power to impart youth to an old and worn-out body. Pope Innocent VIII had the blood of three young men transfused into his veins. But after this operation, he died. As it is quite likely that death was due to a technical accident, perhaps the idea deserves reconsideration. The introduction of young blood into an old organism might bring about favorable changes. It is strange that such an operation has not been tried again. This omission is due, possibly, to the fact that endocrine glands have gained the favor of the physicians. Brown-Séquard, after having injected into himself a fresh extract of testicle, believed that he was rejuvenated. This discovery brought him very great fame. However, he died shortly afterwards. But faith in the testicle as an agent of rejuvenation survived. Steinach attempted to demonstrate that the ligature of its duct stimulates the gland. He performed this operation on many old men. But the results were doubtful. Brown-Séquard's idea was taken up again and extended by Voronoff. The latter, instead of simply injecting testicular extracts, grafted in old men, or men prematurely aged, testicles from chimpanzees. It is incontestable that the operation was followed by an improvement in the general condition and the sexual functions of the patients. But the testicle of a chimpanzee does not live long in a man. During the process of degeneration, it may set free certain secretory products, and these substances, passing into the circulating blood, probably activate the sexual and other endocrine glands of the subject. Such operations do not give lasting results. Old age, as we know, is due to profound modifications of all the tissues and humors, and not to the deficiency of a single gland. The loss of activity of the sexual glands is not the cause of senescence, but one of its consequences. It is probable that neither Steinach nor Voronoff has ever observed true rejuvenation. But their failure does not by any means signify that rejuvenation is forever impossible to obtain.
We can believe that a partial reversal of physiological time will become realizable. Duration, as already mentioned, consists of certain structural and functional processes. True age depends on progressive changes of the tissues and humors. Tissues and humors are one and the same system. If an old man were given the glands of a still-born infant and the blood of a young man, he would possibly be rejuvenated. Many technical difficulties remain to be overcome before such an operation can be undertaken. We have no way of selecting organs suitable to a given individual. There is no procedure for rendering tissues capable of adapting themselves to the body of their host in a definitive manner. But the progress of science is swift. With the aid of the methods already existing, and of those which will be discovered, we must pursue the search for the great secret.
Man will never tire of seeking immortality. He will not attain it, because he is bound by certain laws of his organic constitution. He may succeed in retarding, perhaps even in reversing in some measure, the inexorable advance of physiological time. Never will he vanquish death. Death is the price he has to pay for his brain and his personality. But some day, medicine will teach him that old age, free from diseases of the body and the soul, is not to be feared. To illness, and not to senescence, are due most of our woes.
The human significance of physical time is bound naturally to the nature of inner time. We have already mentioned that physiological time is a flux of irreversible changes of the tissues and humors. It may be approximately measured in special units, each unit being equivalent to a certain functional modification of blood serum. Its characteristics depend on the structure of the organism and on the physiological processes connected with such structure. They are specific of each species, of each individual, and of the age of each individual.
Physiological time is generally referred to physical time, to the time of a clock, inasmuch as we are part of the material world. The natural periods of our life are measured in days or years. Infancy, childhood, and adolescence last about eighteen years. Maturity and old age, fifty or sixty years. Thus, man consists of a brief period of development and of a long period of completion and decay. On the contrary, physical time may be referred to physiological time, and the time of a clock expressed in terms of human duration. Then, a strange phenomenon occurs. Physical time loses the uniformity of its value. The content of a year in units of physiological time becomes variable. It is different for each individual, and for each period of an individual's life.
One perceives, more or less clearly, the changes in the value of physical time, which occur in the course of one's life. The days of our childhood seemed very slow, and those of our maturity are disconcertingly rapid. Possibly we experience this feeling because we unconsciously place physical time in the frame of our duration. And, naturally, physical time seems to vary inversely to it. The rhythm of our duration slows down progressively. Physical time glides along at a uniform rate. It is like a large river flowing through a plain. At the dawn of his life, man briskly runs along the bank. And he goes faster than the stream. Toward midday, his pace slackens. The waters now glide as speedily as he walks. When night falls, man is tired. The stream accelerates the swiftness of its flow. Man drops far behind. Then he stops, and lies down forever. And the river inexorably continues on its course. In fact, the river never accelerates its flow. Only the progressive slackening of our pace is responsible for this illusion. The seeming length of the first part of our existence and the brevity of the last may also be due to the well-known fact that, for the child and for the old man, a year represents quite different proportions of the past. It is more probable, however, that our consciousness vaguely perceives the slowing down of our time, that is, of our physiological processes. And that each one of us runs along the bank and looks at the streaming waters of physical time.
The value of the days of early childhood is very great. Every moment should be utilized for education. The waste of this period of life can never be compensated. Instead of being allowed to grow like plants or little animals, children should be the object of the most enlightened training. But this training calls for a profound knowledge of physiology and psychology, which modern educators have not yet been given the opportunity of acquiring. The declining years of maturity and senescence have little physiological value. They are almost empty of organic and mental changes. They have to be filled with artificial activities. The aging man should neither stop working nor retire. Inaction futher impoverishes the content of time. Leisure is even more dangerous for the old than for the young. To those whose forces are declining, appropriate work should be given. But not rest. Neither should physiological processes be stimulated at this moment. It is preferable to hide their slowness under a number of psychological events. If our days are filled with mental and spiritual adventures, they glide much less rapidly. They may even recover the plenitude of those of youth.
Duration is wedded to man, like the shape to the marble of the statue. Man refers all the events of his world to himself. He uses his span of life as a time unit in his estimation of the age of the earth, of the human race, of civilization, of the length of his own undertakings. Nevertheless, an individual and a nation cannot be placed in the same temporal scale. Social problems should not be considered in the same light as individual ones. They evolve very slowly. Our observations and our experiences are always too short. For this reason, they have little significance. The results of a modification in the material and mental conditions of the existence of a population rarely manifest themselves in less than a century. However, the investigation of the great biological questions is confined to isolated individuals. There is no provision for the continuation of their work when they die. In a like manner, scientific and political institutions are conceived in terms of individual duration. The Roman Catholic Church is the only organization to have realized that the progress of humanity is very slow, that the passing of a generation is an insignificant event in the history of the world. In the evolution of mankind, the duration of the individual is inadequate as a unit of temporal measure. The advent of scientific civilization necessitates a fresh discussion of all fundamental subjects. We are witnessing our own moral, intellectual, and social failure. We have been living under the delusion that democracies would survive through the weak and short-sighted efforts of the ignorant. We begin to understand that they are decaying. Problems involving the future of the great races demand a solution. It is now imperative to prepare for distant events, to mold young generations with a different ideal. The government of nations by men who estimate time in function of their own duration leads, as we well know, to confusion and to failure. We have to stretch our temporal outlook beyond ourselves.
On the contrary, in the organization of transitory social groups, such as a class of children, or a gang of workmen, individual time alone must be taken into account. The members of a group are obliged to work at the same rhythm. The intellectual activity of school children composing a class must be of practically the same standard. In factories, banks, stores, universities, etc., the workers are supposed to accomplish a certain task in a certain time. Those whose strength declines on account of age or illness impede the progress of the whole. So far, human beings are classified according to their chronological age. Children of the same age are placed in the same class. The date of retirement is also determined by the age of the worker. It is known, however, that the true condition of an individual does not depend on his chronological age. In certain types of occupation, individuals should be grouped according to physiological age. Puberty has been used as a way of classifying children in some New York schools. But there are still no means of ascertaining at what time a man should be pensioned. Neither is there any general method of measuring the rate of the organic and mental decline of a given individual. However, physiological tests have been developed by which the condition of a flyer can be accurately estimated. Pilots are retired according to their physiological, and not their chronological, age.
Young and old people, although in the same region of space, live in different temporal worlds. We are inexorably separated by age from one another. A mother never succeeds in being a sister to her daughter. It is impossible for children to understand their parents, and still less their grandparents. Obviously, the individuals belonging to four successive generations are profoundly heterochronic. An old man and his great-grandson are complete strangers. The shorter the temporal distance separating two generations, the stronger may be the moral influence of the older over the younger. Women should be mothers when they are still very young. Thus, they would not be isolated from their children by a temporal gap too great to be bridged, even by love.
From the concept of physiological time derive certain rules of our action on human beings. Organic and mental developments are not inexorable. They can be modified, in some measure, according to our will, because we are a movement, a succession of superposed patterns in the frame of our identity. Although man is a closed world, his outside and inside frontiers are open to many physical, chemical, and psychological agents. And those agents are capable of modifying our tissues and our mind. The moment, the mode, and the rhythm of our interventions depend on the structure of physiological time. Our temporal dimension extends chiefly during childhood, when functional processes are most active. Then, organs and mind are plastic. Their formation can effectively be aided. As organic events happen each day in great numbers, their growing mass can receive such shape as it seems proper to impress permanently upon the individual. The molding of the organism according to a selected pattern must take into account the nature of duration, the constitution of our temporal dimension. Our interventions have to be made in the cadence of inner time. Man is like a viscous liquid flowing into the physical continuum. He cannot instantaneously change his direction. We should not endeavor to modify his mental and structural form by rough procedures, as one shapes a statue of marble by blows of the hammer. Surgical operations alone produce in tissues sudden alterations which are beneficial. And still, recovery from the quick work of the knife is slow. No profound changes of the body as a whole can be obtained rapidly. Our action must blend with the physiological processes, substratum of inner time, by following their own rhythm. For instance, it is useless to administer to a child a large quantity of cod-liver oil in a single dose. But a small amount of this remedy, given each day for several months, modifies the dimensions and the form of the skeleton. Likewise, the mental factors act only in a progressive manner. Our interventions in the building up of body and consciousness have their full effects only when they conform to the laws of our duration.
A child may be compared to a brook, which follows any change in its bed. The brook persists in its identity, in spite of the diversity of its forms. It may become a lake or a torrent. Under the influence of environment, personality may spread and become very thin, or concentrate and acquire great strength. The growth of personality involves a constant trimming of our self. At the beginning of life, man is endowed with vast potentialities. He is limited in his development only by the extensible frontiers of his ancestral predispositions. But at each instant he has to make a choice. And each choice throws into nothingness one of his potentialities. He has of necessity to select one of the several roads open to the wanderings of his existence, to the exclusion of all others. Thus, he deprives himself of seeing the countries wherein he could have traveled along the other roads. In our infancy we carry within ourselves numerous virtual beings, who die one by one. In our old age, we are surrounded by an escort of those we could have been, of all our aborted potentialities. Every man is a fluid that becomes solid, a treasure that grows poorer, a history in the making, a personality that is being created. And our progress, or our disintegration, depends on physical, chemical, and physiological factors, on viruses and bacteria, on psychological influences, and, finally, on our own will. We are constantly being made by our environment and by our self. And duration is the very material of organic and mental life, as it means "invention, creation of forms, continual elaboration of the absolutely new."2
2 Bergson, Henri, loc. cit., 11.
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