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We may learn, and we have learned, many facts concerning these things which are of inestimable value to us in the daily demonstration of our reaction to our surroundings, but this knowledge is based upon an absolute ignorance of the ultimate nature of the very things which we consider most familiar to us. Our knowledge about these things is not of less value to us because we do not know the things. We must simply recognize our ignorance, and also recognize that it is at present incurable. In like manner, we must recognize our inability to define life, while persistently engaged in the study of its nature, of its phenomena under various conditions. We may learn many things about life, just as we may learn many things about matter, or force, or the action of our own minds. The more we try to define life, to try to put into words what it really is, in terms of other fundamentals, themselves as unknowable, the more we are lost. But if we recognize the futility of definitions, and content ourselves here, as in other sciences, with the investigation of phenomena, we may be able to solve some of the problems of living structure.
If we resolve all the phenomena characteristic of life into their primal significance, we will find that every one is a form of reply which each living organism makes to its environment. Every manifestation of energy, every movement, every action of the ingestion of food, of the karyokinetic changes, of the psychical expressions, of developmental changes, both racial and individual; all these and all other manifestations of life are merely the expressions of an answer to environal changes. There is no expression of life or of living substance except such as is brought out in reply to environment. The manifestations of life are not manifestations of some intrinsic energy, -- there is no intrinsic power in life. The protoplasm which is alive has the power, or the quality, or the characteristic, of using in certain manners the forces of the inanimate world. The living protoplasm has no force in itself, any more than any engine has force in itself. This consideration is one of a certain importance. It is not essential that this fact be absolutely granted, but it is essential that every student of the phenomena of health and disease shall understand the nature of the problems which are offered for solution. This consideration rests upon the elemental facts of biological phenomena.
If any cell is to preserve its identity the reply which it makes to its environment must, in a sense, be a selfish one. Every change in the environment must be made a source of energy. Food is a source of energy which is chiefly potential but is also kinetic in some degree. The sunshine, heat, electricity, all that is in the environment of any living cell, may be made a source of either potential or kinetic energy, or may induce a display of energy by stimulating increased metabolism, or it may serve as an energy sparer, either by being a non-conductor of heat, or by serving as a protection from other elements of the environment which might be a source of danger. There is no element in the environment of the cell which may not offer some factors in the problems which the cell has to solve.
Every source of mental energy, even the recognition of the most simple truth, depends upon changes in the environment. For mental strength, the changes in the environment must affect consciousness. The sensory nerves offer the only permeable pathway to the cerebral cortex, and there is at present no physiological basis for considering consciousness as affected in any other manner than by changes in the activity of the nerve cells in the cerebral cortex. It is evident that this activity depends upon the normal metabolism of the cortical neurons. Every power that we possess, every action that we produce, every word and every thought, depend upon these two factors, the changes in environment, and the nature of the reply to these changes. Our own actions are merely the manifestation of forces derived from the physical world and translated into the terms of our own lives. One may write a poem with the strength derived from the oxidation of raw meat ;he may win a battle on toast and milk. The body is no more able to create energy than it is to create matter. There is no magic by means of which the cell or the body of a billion cells may be induced to do ten pounds of work on a six ounce diet, any more than there is some magic by which a fifty dollar clerk can live a hundred dollar life. In either case, the attempt is very apt to result in disaster.
The older schools of practice were built upon a misconception of these facts. It has been supposed from time immemorial that by some priest-craft, or magic, or by the use of various drugs and simples, that the organs of the body might be induced to act more energetically than the state of their nutrition would warrant, and this to the upbuilding of the health of the body. It is true that any of these things may increase the activities far in excess of the energy output warranted by the nutritive condition of the cells of the body. If the cell possesses reserves of the complex molecules wherein are stored the potential energies of the cell, this evolution of energy may not be followed by any serious injury. But if the cells of the body were properly supplied with energy, the need for the drug probably would not be apparent. It is not usual for the normal cell to be subjected to abnormal stimulation. It is true that there are some people who do take medicine to keep themselves well, but these are scarcely to be considered seriously. Under normal conditions, all cells, or nearly all cells, store within their bodies certain substances, variable in nature, which serve as reserves of potential energy. These are alike in some characteristics, though they differ so widely in function. They are all very complex in their molecular structure, and are so unstable that almost any change in the environment of the cell initiates their disintegration, with a corresponding evolution of energy. After these reserves are exhausted, stimulation of the cell may still cause a discharge of energy, but in this case the energy is produced at the expense of the cell structure.
The chromatolysis of the neuron has been very closely studied in this connection. The normal, rested neuron contains granules of a very complex nature, somewhat resembling nuclei in chemical structure, which are recognized only by their staining reactions. In the resting cell these granules, when properly fixed and stained, appear as rather large, angular masses lying in the meshes of the cytoplasm. The form and arrangement of these granules vary in different neurons. They are called Nissl’s granules, after the name of their first describer. Nissl himself called them “tigroid substances.” They are not found in the nucleus, in the axon, nor in a small area around the exit of the axon called the “implantation cone” or “axon hillock.”
In the cell which has been fatigued before death, or poisoned, or subjected to the action of various abnormal conditions, the tigroid substance cannot be demonstrated in any normal manner. If the fatigue has been slight, the change may also be slight. But they are then found in smaller and smaller masses, with more and more difficulty in staining; and, after prolonged fatigue or mal-treatment the granules disappear completely, sometimes not even leaving a diffuse color in the cytoplasm. In these cases of excessive injury, it is doubtful if recovery ever takes place, but very marked loss of the tigroid substance may be followed by recovery if the achromatic substance has been uninjured. That is, the cell is probably able to recover after the loss of all, or nearly all, of the tigroid substance which represents the reserve energy of the neuron, but it is seriously injured, and its ultimate recovery is doubtful, after the intrinsic cell structure is injured. It is very evident that stimulation of the fatigued cell may result in structural changes which are absolutely incurable as the result of an effort to secure the appearance of normal function under abnormal conditions. The neuron that is simply fatigued, even to the point of almost complete destruction of the tigroid masses needs only rest for its recovery; but this same neuron subjected to efficient stimulation, and forced to further evolution of energy may undergo irremediable injury.
The muscles are protected from the effects of over work by the fact that the motor nerve endings are very easily fatigued. The muscle is thus freed from the motor impulses from the central nervous system before it is exhausted. This relationship is not an absolute protection, however, for it is possible for the muscles to remain contracted so long under circumstances of unusual stress, that an atrophy of the muscle results. As a rule, the symptoms of disease do not attract attention until the depletion of the reserves has occurred. An abnormal stimulation may then cause the destructive evolution of energy. The apparent symptoms of the disease are thereby lessened, but ultimate recovery is retarded.
The principle is as true of an excess of the normal stimulation as of the use of the abnormal methods. Persistent overwork, especially under the influence of an emotional strain, is followed by a degree of exhaustion from which recovery is difficult and tedious. The absurdity of trying to overcome such conditions by efforts of the will power is evident. Mental conditions govern, they do not make or destroy energy. Inasmuch as they control many forms of physical activity, they must be considered as important factors in physiology and pathology and therapeutics, but it must not be forgotten that the only source of energy is the environment, and that every cell must be given, in the form of food, or air, or light, all the energy which it displays as muscular work, or nerve impulse, or glandular secretion. It is just as rational to suppose that an amputated limb can be restored by the use of drugs, or by “will power,” as to expect these things to add energy to physiological activities. These things compel the evolution of energy stored in the cell, perhaps as reserve force, perhaps as cell structure; the ultimate effect of this unusual stimulation depends upon the presence or absence of reserve forces. If these be present in sufficient quantity to meet the unusual demands, no greater harm than a waste of energy may result, but if the cells contain little or no reserve force, the reply of the cell must be secured at the expense of cell structure. The process may be compared to the old mills for grinding grain,--if there is no grist and the mill is turned, the mill-stones grind themselves away.
The influence of urgent volitional efforts and of various emotional attitudes upon the cells of the body may be mentioned in this connection. The emotional expressions are coordinated by the neurons of the basal ganglia. The structural relations of these ganglia with the cerebral cortex are such as to render the volitional impulses greatly increased in their power and in their effects upon the metabolism of the body when they are associated with emotional impulses. The effect of these impulses is always to increase katabolism. It is thus much easier for the body to become exhausted in the presence of intense emotional strain than under normal conditions. This is due in part to the partial unconsciousness of bodily conditions associated with emotional stress, but it is chiefly due to the katabolic effect of the emotional impulses themselves. The occurrence of fear, or anger, or what not, does not add energy to the body; it only forces a more complete evolution of energy from the reserve forces of the cells, and, after their exhaustion, from the cell structure itself. The serious prostration which follows urgent effort under conditions of emotional stress is evidence in favor of this view. The use of such simple and apparently harmless stimuli as heat and cold, water of various temperatures, massage, the increase of the patient’s volitional endeavor, may in certain instances, though rarely, initiate an increase of cell activity at the expense of cell structure, and thus retard recovery. The exhaustion produced by the excessive use of these milder forms of stimulation is rarely sufficient to cause more than temporary injury. Note A.—In some instances the use of abnormal forms of stimulation may be of value. In some cases where the normal stimulation is temporarily lacking, some unusual form may be substituted. The most noteworthy instance of this condition is found in cases of nerve injury. If a nerve has been cut, and its regeneration is hoped for, this result is more quickly and certainly secured if the muscles in the area of distribution of the injured nerve be kept in a normal condition. This can only be done by means of exercise. In the absence of nerve impulses, the exercise of the muscles is most efficiently secured by the judicious use of electricity. The muscles thus receive the nearest approach possible to their normal environment.
The relation of Trophic to Nervous Functions in the Neuron, by L. F. Barker, in “The Nervous System.” |