Conclusion
The brain-cells have existed for eons and, amid the vicissitudes of change, they have persisted with perhaps less alteration than has the crust of the earth. Whether in man or in the lower animals, they are related to and obey the same general biologic laws, thus being bound to the entire past and performing their function in accordance with the law of phylogenetic association.
For so long a time have we directed our attention to tumors, infections, and injuries that we have not sufficiently considered the vital force itself. We have viewed each anatomic and pathologic part as an entity and man as an isolated phenomenon in nature. May we not find in the laws of adaptation under natural selection, and of phylogenetic association, the master key that will disclose to us the explanation of many pathologic phenomena as they have already explained many normal phenomena?
And may medicine not correlate the pathologic phenomena of the sick man with the forces of evolution, as the naturalists have correlated the phenomena of the sound man, and thus may not disease, as well as health, be given its evolutionary setting?
PHYLOGENETIC ASSOCIATION IN RELATION TO THE EMOTIONS[*]
[*] Address before the American Philosophical Society, Philadelphia,
April 22, 1911.
The surgeon is familiar with the manifestations of every variety of the human emotions in the various stations of life, from infancy to senility, in health and in disease. Not only does he come into intimate contact with the emotions displayed by the victims of disease and of accidents, but he also observes those manifested by the relatives and friends of the families of his patients. Moreover, he is unhappily forced to notice the emotional effect upon himself when he is waging an unequal battle against death— the strain and worry at a crisis, when a life is in the balance and a single false move may be fatal, is an experience known only to the operating surgeon.
For the data for this paper, therefore, in which I shall for the most part limit my discussion to the strongest of all emotions—FEAR—I have drawn largely from my personal experience as a surgeon, as well as from an experimental research in which I have had the valuable assistance of my associates, Dr. H. G. Sloan, Dr. J. B. Austin, and Dr. M. L. Menten.
I believe it can be shown that it is possible to elicit the emotion of fear only in those animals that utilize a motor mechanism in defense against danger or in escape from it. For example, the defense of the skunk is a diabolic odor which repels its enemies; the skunk has no adequate equipment for defense or escape by muscular exertion, and the skunk therefore shows little or no fear. Again, certain species of snakes are protected by venom; they possess no other means of defense nor have they adequate motor mechanisms for escape and they show no fear. Because of their strength other animals, such as the lion, the grizzly bear, and the elephant, show but little fear (Fig. 6). Animals which have an armored protection, such as the turtle, show little fear. It is, therefore, obvious that fear is not universal and that the emotion of fear is felt only by those animals whose self-preservation is dependent upon an uncertain adequacy of their power of muscular exertion either for defense or for flight (Fig. 7).
What are the principal phenomena of fear? They are palpitation of the heart, acceleration of the rate and alteration of the rhythm of the respiration, cold sweat, rise in body temperature, tremor, pallor, erection of the hair, suspension of the principal functions of digestion, muscular relaxation, and staring of the eyes (Fig. 12). The functions of the brain are wholly suspended except those which relate to the self-protective response against the feared object. Neither the brain nor any other organ of the body can respond to any other lesser stimulus during the dominance of fear.
From these premises it would appear that under the influence of fear, most, perhaps all, of the organs of the body are divided sharply into two classes: First, those that are stimulated, and, second, those that are inhibited. Those that are stimulated are the entire muscular system, the vasomotor and locomotor systems, the senses of perception, the respiration, the mechanism for erecting the hair, the sweat-glands, the thyroid gland, the adrenal gland (Cannon), and the special senses. On the other hand, all the digestive and procreative functions are inhibited. What is the significance of this stimulation of some and inhibition of other organs? As far as we know, the stimulated organs increase the efficiency of the animal for fight or for flight. It is through skeletal muscles that the physical attack or escape is effected; these muscles alone energize the claws, the teeth, the hoofs, and the means for flight. The increased action of the muscles of the heart and the blood-vessels increases the efficiency of the circulation; the secretion of the adrenal gland causes a rise in the blood-pressure; the increased action of the thyroid gland causes an increased metabolic activity; there is evidence that glycogen is actively called out, this being the most immediately available substance for the production of energy; the increased activity of the respiration is needed to supply the greater need of oxygen and the elimination of the increased amount of waste products; the dilatation of the nostrils affords a freer intake of air; the increased activity of the sweat-glands is needed to regulate the temperature of the body which the increased metabolism causes to rise. The activity of all the organs of perception—sight, hearing, smell— is increased in order that the danger may be more accurately perceived. It cannot be a mere coincidence that the organs and the tissues that are stimulated in the emotion of fear are precisely those that are actually utilized in a physical struggle for self-preservation.
Are any other organs stimulated by fear except those that can or that do assist in making a defensive struggle? I know of none. On the other hand, if an animal could dispense with his bulky digestive organs, whose functions are suspended by fear, if he could, so to speak, clear his decks for battle, it would be to his advantage. Although the marvelous versatility of natural selection apparently could devise no means of affording this advantage, it nevertheless shut off the nervous current and saved the vital force which is ordinarily consumed by these non-combatants in the performance of their functions. Whatever may be the origin of fear, its phenomena are due to a stimulation of all the organs and tissues that add to the efficiency of the physical struggle for self-preservation and an inhibition of the func-
{illust. caption = FIG. 19—THE BROAD JUMP. Note the similarity of the expression to the facial expression of fear and of anger (Figs. 12 and 21). (Wm. J. Brownlow, drawn from photo.) tions of the leading organs that do not participate in that struggle— the non-combatants, so to speak. Fear arose from injury, and is one of the oldest and surely the strongest emotion. By the slow process of vast empiricism nature has evolved the wonderful defensive motor me-chanism of many animals and of man. The stimulation of this mechanism leading to a physical struggle is action, and the stimulation of this mechanism without action is emotion. We may say, therefore, that fear is a PHYLOGENETIC FIGHT OR FLIGHT (Fig. 18). On this hypothesis all the organs and parts {illust. caption = FIG. 20.-FINISH OF RELAY RACE.
Compare the facial expression of the runners with those in Figs. 12, 19, 22. These pictures illustrate the fact that the same mechanism is stimulated in emotion as in physical action. (Photo by Underwood and Underwood, N. Y.)}
of the body are integrated, connected, or correlated for the self-preservation of the individual by the activity of his motor mechanism (Figs. 12, 19, and 20). We fear not in our hearts alone, not in our brains alone, not in our viscera alone—fear influences every organ and tissue; each organ or tissue is stimulated or inhibited according to its use or hindrance in the physical struggle for existence. By thus concentrating all or most of the nerve force on the nerve-muscular mechanism for defense, a greater physical power is developed. Hence it is that under the stimulus of fear animals are able to perform preternatural feats of strength. For the same reason, the exhaustion following fear will be increased as the powerful stimulus of fear drains the cup of nervous energy even though no visible action may result. An animal under the stimulus of fear may be likened to an automobile with the clutch thrown out but whose engine is racing at full speed. The gasoline is being consumed, the machinery is being worn, but the machine as a whole does not move, though the power of its engine may cause it to tremble.
When this conception is applied to the human beings of today, certain mysterious phenomena are at once elucidated. It must be borne in mind that man has not been presented with any new organs to meet the requirements of his present state of civilization; indeed, not only does he possess organs of the same type as those of his savage fellows, but of the same type also as those possessed by the lower animals even. In fact, man has reached his present status of civilization with the primary equipment of brutish organs. Perhaps the most striking difference between man and animals lies in the greater control which man has gained over his primitive instinctive reactions. As compared with the entire duration of organic evolution, man came down from his arboreal abode and assumed his new role of increased domination over the physical world but a moment ago. And now, though sitting at his desk in command of the complicated machinery of civilization, when he fears a business catastrophe his fear is manifested in the terms of his ancestral physical battle in the struggle for existence. He cannot fear intellectually, he cannot fear dispassionately, he fears with all his organs, and the same organs are stimulated and inhibited as if, instead of it being a battle of credit, of position, or of honor, it were a physical battle with teeth and claws. Whether the cause of acute fear be moral, financial, social, or stage fright, the heart beats wildly, the respirations are accelerated, perspiration is increased, there are pallor, trembling, indigestion, dry mouth, etc. The phenomena are those which accompany physical exertion in self-defense or escape. There is not one group of phenomena for the acute fear of the president of a bank in a financial crash and another for the hitherto trusted official who suddenly and unexpectedly faces the imminent probability of the penitentiary; or one for a patient who unexpectedly finds he has a cancer and another for the hunter when he shoots his first big game. Nature has but one means of response to fear, and whatever its cause the phenomena are always the same—always physical.
If the stimulus of fear be repeated from day to day, whether in the case of a mother anxious on account of the illness of a child; a business man struggling against failure; a politician under contest for appointment; a broker in the daily hazard of his fortune; litigants in legal battle, or a jealous lover who fears a rival; the countless real as well as the baseless fears in daily life, in fact, all forms of fear, as it seems to me, express themselves in like terms of ancestral physical contests. On this law, fear dominates the various organs and parts of the body.
Anger and fear express opposite emotional states. Fear is the expression of a strong desire to escape from danger; anger, of a strong desire to attack physically and to vanquish opposition. This hypothesis is strongly supported by the outward expressions of fear and of anger. When the business man is conducting a struggle for existence against his rivals, and when the contest is at its height, he may clench his fists, pound the table, perhaps show his teeth, and exhibit every expression of physical combat. Fixing the jaw and showing the teeth in anger merely emphasize the remarkable tenacity of phylogeny. Although the development of the wonderful efficiency of the hands has led to a modification of the once powerful canines of our progenitors, the ancestral use of the teeth for attack and defense is attested in the display of anger. In all stations of life differences of opinion may lead to argument and argument to physical combats, even to the point of killing. The physical violence of the savage and of the brute still lies surprisingly near the surface (Fig. 21).
We have now presented some of the reasons based largely on gross animal behavior why fear is to be regarded as a response to phylogenetic association with physical danger. In further support of this hypothesis, I shall now present some clinical and experimental evidence. Although there is not convincing proof, yet there is evidence that the effect of the stimulus of fear upon the body when unaccompanied by physical activity is more injurious than is an actual physical contest which results in fatigue without gross physical injury. It is well known that the soldier who, while under fire, waits in vain for orders to charge, suffers more than the soldier who flings himself into the fray; and that a wild animal endeavoring to avoid capture suffers less than one cowering in captivity. An unexpressed smouldering emotion is measurably relieved by action. It is probable that the various energizing substances needed in physical combat, such as the secretions of the thyroid, the adrenals (Cannon), etc., may cause physical injury to the body when they are not consumed by action (Fig. 22).
That the brain is definitely influenced—damaged even— by fear has been proved by the following experiments: Rabbits were frightened by a dog but were neither injured nor chased. After various periods of time the animals were killed and their brain-cells compared with the brain-cells of normal animals— wide-spread changes were seen (Fig. 13). The principal clinical phenomena expressed by the rabbit were rapid heart, accelerated respiration, prostration, tremors, and a rise in temperature. The dog showed similar phenomena, excepting that, instead of such muscular relaxation as was shown by the rabbit, it exhibited aggressive muscular action. Both the dog and the rabbit were exhausted but, although the dog exerted himself actively and the rabbit remained physically passive, the rabbit was much more exhausted.
Further observations were made upon the brain of a fox which had been chased for two hours by members of a hunt club, and had been finally overtaken by the hounds and killed. Most of the brain-cells of this fox, as compared with those of a normal fox, showed extensive physical changes (Fig. 4).
The next line of evidence is offered with some reservation, but it has seemed to me to be more than mere idle speculation. It relates to the phenomena of one of the most interesting diseases in the entire category of human ailments—I refer to exophthalmic goiter, or Graves' disease, a disease primarily involving the emotions. This disease is frequently the direct sequence of severe mental shock or of a long and intensely worrying strain. The following case is typical: A broker was in his usual health up to the panic of 1907; during this panic his fortune and that of others were for almost a year in jeopardy, failure finally occurring. During this heavy strain he became increasingly nervous and by imperceptible degrees there developed a pulsating enlargement of the thyroid gland, an increased prominence of the eyes, marked increase in perspiration—profuse sweating even—palpitation of the heart, increased respiration with frequent sighing, increase in blood-pressure; there were tremor of many muscles, rapid loss of weight and strength, frequent gastro-intestinal disturbances, loss of normal control of his emotions, and marked impairment of his mental faculties. He was as completely broken in health as in fortune. These phenomena resembled closely those of fear and followed in the wake of a strain which was due to fear.
In young women exophthalmic goiter often follows in the wake of a disappointment in love; in women, too, it frequently follows the illnesses of children or parents during which they have had to endure the double strain of worry and of constant care. Since such strains usually fall most heavily upon women, they are the most frequent victims of this disease. Now, whatever the exciting cause of exophthalmic goiter, whether it be unusual business worry, disappointment in love, a tragedy, or the illness of a loved one, the symptoms are alike and closely resemble the phenomena of one of the great primitive emotions. How could disappointment in love play a role in the causation of Graves' disease? If the hypothesis which has been presented as an explanation of the genesis and the phenomena of fear be correct, then that hypothesis explains also the emotion of love. If fear be a phylogenetic physical defense or escape which does not result in muscular action, then love is a phylogenetic conjugation without physical action. The quickened pulse, the leaping heart, the accelerated respiration, the sighing, the glowing eye, the crimson cheek, and many other phenomena are merely phylogenetic recapitulations of ancestral acts. The thyroid gland is believed to participate in such physical activities. Hence it may well follow that the disappointed maiden who is intensely integrated for a youth will, at every thought of him, be subjected by phylogenetic association to a specific stimulation analogous to that which attended the ancestral consummation. Moreover, a happy marriage has many times been followed by a cure of the exophthalmic goiter which appeared in the wake of such an experience.
The victims of Graves' disease present a counterpart of emotional exhaustion. That the emotions in Graves' disease are abnormally acute is illustrated by my personal observation of the death of a subject of this disease from fear alone. Whatever the exciting cause of this disease, the symptoms are the same; just as in fear, the phenomena are the same whatever the exciting cause.
Figures 12 and 16 show the resemblance between the outward appearances of a patient with Graves' disease and of a person obsessed by fear. Fear and Graves' disease have the following phenomena in common: Increased heart-beat, increased respiration, rising temperature, muscular tremors, protruding eyes, loss in weight; Cannon has found an increased amount of adrenalin in the blood in fear and Frankel in Graves' disease; increased blood-pressure; muscular weakness; digestive disturbances; impaired nervous control; hypersusceptibility to stimuli; in protracted intense fear the brain-cells show marked physical changes, and in Graves' disease analogous changes are seen (Figs. 13 C and 15). In Graves' disease there seems to be a composite picture of an intense expression of the great primitive emotions. If Graves' disease be a disease of the great primitive emotions, or rather of the whole motor mechanism, how is the constant flow of stimulation of this complicated mechanism supplied? It would seem that there must be secreted in excessive amount some substance that activates the motor mechanism. The nervous system in Graves' disease is hypersusceptible to stimuli and to thyroid extract. It might follow that even a normal amount of thyroid secretion would lead to excessive stimulation of the hypersusceptible motor mechanism.
This condition of excessive motor activity and hyperexcitability may endure for years. What is the source of this pathologic excitation? The following facts may give a clue. In suitable cases of Graves' disease, if the thyroid secretion is sufficiently diminished by a removal of a part of the gland or by interrupting the nerve and the blood supply, the phenomena of the disease are diminished immediately, and in favorable cases the patient is restored to approximately the normal condition. The heart action slows, the respiratory rate falls, the restlessness diminishes, digestive disturbances disappear, tremors decrease, there is a rapid increase in the body weight, and the patient gradually resumes his normal state. On the other hand, if for a period of time extract of the thyroid gland is administered to a normal individual in excessive dosage, there will develop nervousness, palpitation of the heart, sweating, loss of weight, slight protrusion of the eyes, indigestion; in short, most of the phenomena of Graves' disease and of the strong emotions will be produced artificially (Figs. 15 and 23). When the administration of the thyroid extract is discontinued, these phenomena may disappear. On the other hand, when there is too little or no thyroid gland, the individual becomes dull, stupid, and emotionless, though he may be irritable; while if a sufficient amount of thyroid extract be given to such a patient he may be brought back to his normal condition.
Hence we see that the phenomena of the emotions may within certain limits be increased, diminished, or abolished by increasing, diminishing, or totally excluding the secretion of the thyroid gland.
Graves' disease may be increased by giving thyroid extract and by fear. It may be diminished by removing a part of the gland, or by interrupting the blood and nerve supply, or by complete rest. In addition, at some stage of Graves' disease there is an increase in the size and in the number of the secreting cells. These facts regarding the normal and the pathologic supply of thyroid secretion point to this gland as one of the sources of the energizing substance or substances, by means of which the motor phenomena of animals are executed and their emotions expressed.
Anger is similar to fear in origin and, like fear, is an integration and stimulation of the motor mechanism and its accessories. Animals which have no natural weapons for attack experience neither fear nor anger, while the animals which have weapons for attack express anger principally by energizing the muscles used in attack. Although, as has already been stated, the efficiency of the hands of man has largely supplanted the use of the teeth, he still shows his teeth in anger and so gives support to the theory that this emotion is of remote ancestral origin and proves the great persistence of phylogenetic association. On this conception we can understand why it is that a patient consumed by worry—which to me signifies interrupted stimulation, a state of alternation between hope and fear—suffers so many bodily impairments and diseases even. This hypothesis explains the slow dying of animals in captivity. It explains the grave digestive and metabolic disturbances which appear under any nerve strain, especially under the strain of fear, and the great benefits of confidence and hope; it explains the nervousness, loss of weight, indigestion—in short, the comprehensive physical changes that are wrought by fear and by sexual love and hate. On this hypothesis we can understand the physical influence of one individual over the body and personality of another; and of the infinite factors in environment that, through phylogenetic association, play a role in the functions of many of our organs. It is because under the uncompromising law of survival of the fittest we were evolved as motor beings that we do not possess any organs or faculties which have not served our progenitors in accomplishing their survival in the relentless struggle of organic forms with one another. We are now, as we were then, essentially motor beings, and the only way in which we can meet the dangers in our environment is by a motor response. Such a motor response implies the integration of our entire being for action, this integration involving the activity of certain glands, such as the adrenals (Cannon), the thyroid, the liver, etc., which throw into the blood-stream substances which help to form energy, but which, if no muscular action ensues, are harmful elements in the blood. While this motor preparation is going on, the entire digestive tract is inhibited. It thus becomes clear why an emotion is more harmful than action.
Any agency that can sufficiently inspire faith,—dispel worry,— whether that agency be mystical, human, or divine, will at once stop the body-wide stimulations and inhibitions which cause lesions which are as truly physical as is a fracture. The striking benefits of good luck, success, and happiness; of a change of scene; of hunting and fishing; of optimistic and helpful friends, are at once explained by this hypothesis. One can also understand the difference between the broken body and spirits of an animal in captivity and its buoyant return to its normal condition when freed.
But time will not permit me to follow this tempting lead, which has been introduced for another purpose—the proposal of a remedy.
Worries either are or are not groundless. Of those that have a basis, many are exaggerated. It has occurred to me to utilize as an antidote an appeal to the same great law that originally excited the instinctive involuntary reaction known as fear— the law of self-preservation.
I have found that if an intelligent patient who is suffering from fear can be made to see so plainly as to become firmly convinced that his brain, his various organs, indeed his whole being, could be physically damaged by fear, that this same instinct of self-preservation will, to the extent of his conviction, banish fear. It is hurling a threatened active militant danger, whose injurious influences are both certain and known, against an uncertain, perhaps a fancied, one. In other words, fear itself is an injury which when recognized is instinctively avoided. In a similar manner anger may be softened or banished by an appeal to the stronger self-preserving instinct aroused by the fear of physical damage, such as the physical injury of brain-cells. This playing of one primitive instinct against another is comparable to the effect produced upon two men who are quarreling when a more powerful enemy of both comes threateningly on the scene.
The acute fear of a surgical operation may be banished by the use of certain drugs that depress the associational power of the brain and so minimize the effect of the preparations that usually inspire fear. If, in addition, the entire field of operation is blocked by local anesthesia so that the associational centers are not awakened, the patient will pass through the operation unscathed.
The phylogenetic origin of fear is injury, hence injury and fear cause the same phenomena. In their quality and in their phenomena psychic shock and traumatic shock are the same. The perception of danger by the special senses in the sound of the opening gun of a battle, or in the sight of a venomous snake, is phylogenetically the same and causes the same effects upon the entire body as an operation under anesthesia or a physical combat in that each drives the motor mechanism. The use of local anesthetics in the operative field prevents nerve-currents from the seat of injury from reaching the brain and there integrating the entire body for a self-defensive struggle. The result, even though a part of the brain is asleep and the muscles paralyzed, is the same as that produced by the interception of the terrifying sound of the gun, or of the sight of the dangerous reptile, since the stimulation of the motor mechanism is prevented.
By both the positive and the negative evidence we are forced to believe that the emotions are primitive instinctive reactions which represent ancestral acts; and that they therefore utilize the complicated motor mechanism which has been developed by the forces of evolution as that best adapted to fit the individual for his struggle with his environment or for procreation.
The mechanism by which the motor acts are performed and the mechanism by which the emotions are expressed are one and the same. These acts in their infinite complexity are suggested by association— phylogenetic association. When our progenitors came in contact with any exciting element in their environment, action ensued then and there. There was much action—little restraint or emotion. Civilized man is really in auto-captivity. He is subjected to innumerable stimulations, but custom and convention frequently prevent physical action. When these stimulations are sufficiently strong but no action ensues, the reaction constitutes an emotion. A phylogenetic fight is anger; a phylogenetic flight is fear; a phylogenetic copulation is sexual love, and so one finds in this conception an underlying principle which may be the key to an understanding of the emotions and of certain diseases.
PAIN, LAUGHTER, AND CRYING[*]
[*] Address delivered before the John Ashhurst, Jr.. Surgical Society of the University of Pennsylvania, May 3, 1912.
PAIN
Pain, like other phenomena, was probably evolved for a particular purpose— surely for the good of the individual; like fear and worry, it frequently is injurious. What then may be its purpose?
We postulate that pain is one of the phenomena which result from a stimulation to motor action. When a barefoot boy steps on a sharp stone it is important that the injuring contact be released as quickly as possible; and therefore physical injury pain results and impels the required action. Anemia of the soft parts at the points of pressure results from prolonged sitting or lying in one position, and as a result pain compels a muscular action that shifts the damaging pressure—this is the pain of anemia; when the rays of the blazing sun shine directly upon the retina, pain immediately causes a protective muscular action—the lid is closed, the head turns away—this is light pain; when standing too close to a blazing fire the excessive heat causes a pain which results in the protective muscular action of moving away—this is heat pain; when the urinary bladder is acutely overdistended the resultant pain induces voluntary as well as involuntary muscular contraction— this is evacuation pain; associated with defecation is a characteristic warning pain, and an active pain which induces the required muscular action—this, like the pain accompanying micturition, is an evacuation pain; in obstruction of the urinary passages and of the large and the small intestine the pain is exaggerated, as is the accompanying muscular contraction—this is a pathologic evacuation pain; when the fetus reaches full term and labor is to begin, it is heralded by pain which is associated with rhythmic contractions of the uterine muscle; later, many other muscles take part in the birth and pain is associated with all these muscular contractions—these are labor pains; when a foreign body, be it ever so small, falls upon the conjunctiva or cornea there results what is perhaps the acutest pain known, and quick and active muscular action follows—this is special contact pain. Special pain receptors are placed in certain parts of the nose, the pharynx, and the larynx, the stimulation of which causes special motor acts, such as sneezing, hawking, coughing. Curiously vague pains are associated with the protective motor act of vomiting and with the sexual motor acts—these may be termed nausea pains and pleasure pains. We now see, therefore, that against the injurious physical contacts of environment, against heat and cold, against damaging sunlight, against local anemia when resting or sleeping, the body is protected by virtue of the muscular action which results from pain. Then, too, for the emptying of the pregnant uterus, for the evacuation of the intestine and of the urinary bladder as normal acts, and for the overcoming of obstructions in these tracts, pain compels the required muscular actions, For passing gall-stones and urinary calculi, urgent motor stimuli are awakened by pain. For each of these diversified pains the consequent muscular action is specific in type, distribution, and intensity. This statement is so commonplace that we are apt to miss the significance and the wonder of it. It is probable that every nerve-ending in the skin and every type of stimulation represents a separate motor pattern, the adequate stimulation of which causes always the same response.
Let us pass on to the discussion of another and perhaps even more interesting type of pain, that associated with infection. Not all kinds of infection are painful; and in those infections that may be associated with pain there is pain only when certain regions of the body are involved. Among the infections that are not associated with pain are scarlet fever, typhoid fever, measles, malaria, whooping-cough, typhus fever, and syphilis in its early stages. The infections that are usually, though not always, associated with pain are the pyogenic infections. The pyogenic infections and the exanthemata constitute the great majority of infections and are the basis of the discussion which follows.
I will state one of my principal conclusions first, i. e., that the only types of infection that are associated with pain are those in which the infection may be spread by muscular action or those in which the fixation of parts by continued muscular rigidity is an advantage; and, further, as a striking corollary, that the type of infection that may cause muscular action when it attacks one region of the body may cause no such action when it attacks another region.
The primary, and perhaps the most striking, difference between the painless exanthemata and the painful pyogenic infections is that in the case of the exanthemata the protective response of the body is a chemical one,—the formation of antibodies in the blood, which usually produce permanent immunity,—while the response to the pyogenic infections is largely phagocytic. In the pyogenic infections, in order to protect the remainder of the body, which, of course, enjoys no immunity, every possible barrier against the spread of the infection is thrown about the local point of infection. How are these barriers formed? First, lymph is poured out, then the part is fixed by the continuous contraction of the neighboring muscles and by the inhibition of those muscles that, in the course of their ordinary function, would by their contractions spread the infection. Wherever there is protective muscular rigidity there is also pain. On the other hand, in pyogenic infections in the substance of the liver, in the substance of the kidney, within the brain, in the retroperitoneal space, in the lobes of the lung, in the chambers of the heart and in the blood-vessels of the chest and the abdomen, in all locations in which muscular contractions can in no way assist in localizing the disease, pyogenic infections produce no muscular rigidity and no pain. Apparently, therefore, only those infections are painful which are associated with a protective muscular contraction. This explains why tuberculosis of the hip is painful, while tuberculosis of the lung is painless.
There is a third type of pain which modifies muscular action in a curious way. We have already stated that local pain serves an adaptive purpose. In this light let us now consider headache. Headache is one of the commonest initiatory symptoms of the various infections, especially of those infections which are accompanied by no local pain and by no local muscular action. In peritonitis, cholecystitis, pleurisy, arthritis, appendicitis, salpingitis, child-birth, in obstructions of the intestinal and the genito-urinary tract, in short, in those acute processes in which the local symptoms are powerful enough to govern the individual as a whole,—to make him lie down and keep quiet, refuse food and possibly reject what is already in the stomach,— in all these conditions there is rarely a headache, but in the diseases in which local pain is absent, such as the exanthemata, typhoid fever, and auto-intoxication, which have no dominating local disturbances to act as policemen to put the individual to bed and to make him refuse food that he may be in the most favorable position to combat the oncoming disease, in such cases in which these masterful and beneficent local influences are absent we postulate that headache has been evolved to perform this important service.
On the hypothesis that it is good for the individual who is acutely stricken by a disease or who is poisoned by autointoxication to rest and fast, and that the muscular system obeys the imperial command of pain, and in view of the fact that the brain is not only in constant touch with the conditions of every part of the body but that it is also the controlling organ of the body, one would expect that in these diseases the major pain whose purpose it is to govern general muscular action would be located in the head and there we find it. How curious and yet how intelligible is the fact that, though a headache may be induced by even a slight auto-intoxication, an abscess may exist within the brain without causing pain. When an obliterative endarteritis is threatening a leg with anemic gangrene, or when one lies too long in the same position on a hard bed, there is threatening injury from local anemia, and as a result there is acute pain, but when the obliterative endarteritis threatens anemia of the brain, or when an embolism or thrombosis has produced anemia of the brain, there may be no accompanying pain. The probable explanation of the pain which results in the first instance and the lack of pain in the second is that in the former muscular action constitutes a self-protective response, but in the other it does not. Diseases and injuries of the brain are notoriously difficult to diagnosticate. This may well be because it has always been so well protected by the skull that there have been evolved within it few tell-tale self-protective responses, so that in the presence of injury and disease within itself the brain remains remarkably silent. It should occasion no surprise that there are in the brain no receptors, the mechanical stimulation of which can cause pain, because its bony covering has always prevented the adaptive implantation within it of contact pain receptors. Dr. Frazier tells me that in the course of his operations on the brains of unanesthetized patients he is able to explore the entire brain freely and without pain. From my own experience I am able to confirm Dr. Frazier's observation. In addition, the two-stage operation for the excision of the Gasserian ganglion provides an observation of extraordinary interest. If at the first seance the ganglion is exposed, but is not disturbed except by the iodoform gauze packing, then on the following day the gauze may be removed, the ganglion picked up, and its branches and root excised without anesthesia and without pain. The same statement and explanation may be made regarding the distribution of pain receptors for physical contact within the parenchyma of the liver, the gall-bladder, the abdominal viscera, the spleen, the heart, the lungs, the retroperitoneal tissue, the deep tissue of the back, the vertebrae, and in certain portions of the spinal cord. Just what is the distribution of the receptors for heat and for cold I am unable to state, but this much we do know, that without anesthesia the intestines may be cauterized freely without the least pain resulting, and in animals the cauterization of the brain causes no demonstrable change in the circulatory or respiratory reactions. It is probable therefore that the distribution of the pain receptors for physical contact and for heat are limited to those parts of the body that have been exposed to injurious contacts with environment.
Of special significance is the pain which is due to cold, which increases muscular tone and produces shivering. The general increase in muscular tone produces an interesting postural phenomenon: the limbs are flexed and the body bent forward, a position which probably is due to the fact that the flexors are stronger than the extensors. As muscular action is always accompanied by heat production, the purpose of the muscular contraction and the shivering is quite certainly caused by cold to assist in the maintenance of the normal body temperature.
We have now discussed many of the causes of pain and in each instance we have found an associated muscular action which apparently serves some adaptive purpose (Figs. 24 and 25). If we assume that pain exists for the purpose of stimulating muscular reactions, we may well inquire what part of the nervous are is the site of the sensation of pain—the nerve-endings, the trunk, or the brain? Does pain result from physical contact with the nerve-endings, with the physical act of transmitting an impression along the nerve trunk, or with the process within the brain-cells by which energy is released to cause a motor act?
It seems most probable that the site of the pain is in the brain-cells. If this be so, then what is the physical process by which the phenomena of pain are produced? The one hypothesis that can be tested experimentally is that pain is a phenomenon resulting from the rapid discharge of energy in the brain-cells. If this be true, then if every pain receptor of the body were equally stimulated in such a manner that
{illust. caption = FIG. 25.—FEAR AND AGONY. "Amid this dread exuberance of woe ran naked spirits wing'd with horrid fear."— Dante's "Inferno," Canto XXIV, lines 89, 90. all the stimuli reached the brain-cells simultaneously, the cells would find themselves in equilibrium and no motor act would be performed. But if all the pain receptors of the body but one were equally stimulated, and this one stimu-lated harder than the rest, then the latter would gain possession of the final common path, the sensation of pain would be felt, and a muscular contraction would result. It is well known that when a greater pain is thrown into competition with a lesser one, the lesser is completely submerged. In this manner the school-boy initiates the novice into the mystery of the painless plucking of hair. The simultaneous, but severe application of the boot to the blindfolded victim takes complete and exclusive possession of the final common path and the hair is painlessly plucked through the triumph of the boot stimulus over the hair stimulus in the struggle for the possession of the final common path. Another argument in favor of this hypothesis that pain is an accompaniment of the release of energy in the brain- cells is found in the fact that painless stimuli received through the special senses may completely submerge the painful stimuli of physical injury; for although the stimuli to motor action, which are received through the senses of sight, hearing, and smell, cause even more powerful motor action than those caused by physical contact stimuli, yet they are not accompanied by pain. Examples of this triumph of stimulation of the special senses over contact stimulation are frequently seen in persons obsessed by anger or fear, and to a less degree in those obsessed by sexual emotion. In the fury of battle the soldier may not perceive his wound until the emotional excitation is wearing away, when the sensation of warm blood on the skin may first attract his attention. Religious fanatics are said to feel no pain when they subject themselves to self-injury. Now, since both psychic and mechanical stimuli cause motor action by the excitation ofprecisely the same mechanism in the brain, and since the more rapid release of energy from psychic stimuli submerges the physical stimuli and prevents pain, it would seem that pain must be a phenomenon which is associated with the process of releasing energy by the brain-cells. Were physical injury inflicted in a quiescent state equal to that inflicted in the emotional state, great pain and intense muscular action would be experienced. Now the emotions are as purely motor excitants as is pain. The dynamic result is the same the principal difference being the greater suddenness and the absolute specificity of the pain stimuli as compared with the more complex and less peremptory stimuli of the emotions. A further evidence that pain is a product of the release of brain-cell energy is the probability that if one could pierce the skin at many points on a limb in such a manner that antagonistic points only were equally and simultaneously stimulated, then an equilibrium in the governing brain- cells would be established and neither pain nor motion would follow. An absolute test of this assumption cannot be made but it is supported by the obtainable evidence. We will now turn to a new viewpoint, a practical as well as a fascinating one, which can best be illustrated by two case histories: A man, seventy-eight years old, whose chief complaint was obstinate constipation, was admitted to the medical ward of the Lakeside Hospital several years ago. The abdomen was but slightly distended; there was no fever, no increased leukocytosis, no muscular rigidity, and but slight general tenderness. He claimed to have lost in weight and strength during the several months previous to his admission. A tentative diagnosis of malignant tumor of the large intestine was made, but free movements weresecured rather easily, and we abandoned the idea of an exploratory operation. The patient gradually failed and died without a definite diagnosis having been made by either the medical or the surgical service. At autopsy there was found a wide-spread peritonitis arising from a perforated appendix. A child, several years old, was taken ill with some indefinite disease. A number of the ablest medical and surgical consultants of a leading medical center thoroughly and repeatedly investigated the case. Although they could make no definite diagnosis they all agreed that the trouble surely could not be appendicitis because there was neither muscular rigidity nor tenderness. The autopsy showed a gangrenous appendix and general peritonitis. How can these apparently anomalous cases be explained? These two cases are illustrations of the same principle that underlies the freedom from pain which results from the use of narcotics and anesthetics, the same principle that explains the fact that cholecystitis may occur in the aged without any other local symptoms than the presence of a mass and perhaps very slight tenderness; and that accounts in general for the lack of well-expressed disease phenomena in senility and in infancy. The reason why the aged, the very young, and the subjects of general paresis show but few symptoms of disease is that in senility the brain is deteriorated, while in infancy the brain is so undeveloped that the mechanism of association is inactive, hence pain and tenderness, which are among the oldest of the associations, are wanting. Senility and infancy are by nature normally narcotized. The senile are passing through the twilight into the night; while infants are traversing through the dawn into the day. Hence it is that the diagnosis of injury and disease in the extremes oflife is beset by especial difficulties, since the entire body is as silent as are the brain, the pericardium, the mediastinum, and other symptomless areas. For the same reason, when a patient who is seriously ill with a painful disease turns upon the physician a glowing eye and an eager face, and remarks how comfortable he feels, then the end is near. This is a brilliant and fateful clinical mirage. When one reflects on the vast amount of evidence as to the origin and the purpose of pain, he is forced to conclude that pain is a phenomenon of motor stimulation, and that its principal role is the protection of the individual against the gross and the microscopic enemies in his environment. The benefits of pain are especially manifested in the urgent muscular actions by means of which the body moves away from physical injury; obstructions of the hollow viscera are overcome; rest is compelled in the acute infections— the infected points are held rigidly quiet, the muscles of the abdomen are fixed, and harmful peristalsis is arrested in peritonitis; while there is absolutely no pain in the diseases or injuries which affect those regions of the body in which in the course of evolution no pain receptors were placed, or in those diseases in which muscular inhibition or contraction is of no help. In a biologic sense pain is closely associated with the emotional stimuli, for both pain and the emotions incite motor activity for the good of the individual. The frequent occurrence of post-operative and post- traumatic pain is accounted for by the fact that the operation or the injury has lowered the threshold of the brain- cells to trauma; the brain and not the local sensitive field is the site of the pain. I have found that, by blockingthe field of operation with local anesthesia, post-operative pain is diminished; that is, since the local anesthesia prevents the strong stimuli of the trauma from reaching the brain, its threshold is not lowered. There is a close resemblance between the phenomena of pain habit, of education, of physical training, of love and of hate. In education, in pain habit, in all emotional relations, a low brain- cell threshold is established which facilitates the reception of specific stimuli; all these processes are motor acts, or are symbolic of motor acts, and we may be trained to perceive misfortune and pain as readily as we are trained to perceive mathematical formulae or moral precepts. In each and every case, readiness of perception depends, as it seems to me, upon a modified state of the brain-cells, their threshold especially, the final degree of perception possible in any individual being perhaps based on the type of potential molecules of which the brain is built. We must believe also that every impression is permanent, as only thus could an individual animal or a man be fitted by his own experience for life's battles. LAUGHTER AND CRYING What is laughter? What is its probable origin, its distribution, and its purpose? Laughter is an involuntary rhythmic contraction of certain respiratory muscles, usually accompanied by certain vocal sounds. It is a motor act of the respiratory apparatus primarily, although if intense it may involve not only the extraordinary muscles of respiration, but most of the muscles of the body. There are many degrees of laughter, from the mere brightening of the eyes, a fleeting smile, tittering andgiggling, to hysteric and convulsive laughter. Under certain circumstances, laughter may be so intense and so long continued that it leads to considerable exhaustion. The formation of tears is sometimes associated with laughter. When integrated with laughter, the nervous system can perform no other function. Crying is closely associated with laughter, and in children especially laughter and crying are readily interchanged. We postulate that laughter and weeping serve a useful purpose. According to Darwin, only man and monkeys laugh (Fig. 26); other animals exhibit certain types of facial expression accompanying various emotions, but laughter in the sense in which that word is commonly used is probably an attribute of the primates only, although it is probable that many animals find substitutes for laughter. The proneness of man to laughter is modified by age, sex, training, mental state, health, and by many other factors. Healthy, happy children are especially prone to laughter, while disease, strong emotions, fatigue, and age diminish laughter. Women laugh more than do men. The healthy, happy maturing young woman perhaps laughs most, especially when she is slightly embarrassed. What causes laughter? Good news, high spirits, tickling, hearing and seeing others laugh; droll stories; flashes of wit; passages of humor; averted injury; threatened breach of the conventions; and numerous other causes might be added. It is obvious that laughter may be produced by diverse influences, many of which are so unlike each other that it would at first sight seem improbable that a single general principle underlies all. Before presenting a hypothesis which harmonizes most of the facts, and which mayoffer an explanation of the origin and purpose of laughter, let us return for a moment to some previous considerations— that man is essentially a motor being; that all his responses to the physical forces of his environment are motor; {illust. caption = FIG. 26.—LAUGHING CHIMPANZEE. "Mike," the clever chimpanzee in the London Zoo, evidently enjoys a joke as well as any one else. (Photo by Underwood and Underwood, N. Y.)}
that thoughts and words even are symbolic of motor acts; that in the emotions of fear, of anger, and of sexual love the whole body is integrated for acts which are not performed. These integrations stimulate the brain-cells, the ductless glands, and other parts, and the energizing secretions, among which are epinephrin, thyroid and hypophyseal secretions, are thrown into the blood-stream, while that most available fuel, glycogen, is also mobilized in the blood. This body-wide preparation for action may be designated kinetic reaction. The fact that emotion is more injurious to the body than is muscular action is well known, the difference being probably caused by the fact that when there is action the above-mentioned products of stimulation are consumed, while in stimulation without action they are not consumed and must be eliminated as waste products. Now these activating substances and the fuel glycogen may be consumed by any muscular action as well as by the particular muscular action for which the integration and consequent stimulation were made; that is, if one were provoked to such anger that he felt impelled to attack the object of his anger, one of three things might happen: First, he might perform no physical act but give expression to the emotion of anger; second, he might engage in a physical struggle and completely satisfy his anger; third, he might immediately engage in violent gymnastic exercises and thus consume all the motor-producing elements mobilized by the anger and thus clarify his body.
In these premises we find our explanation of the origin and purpose of laughter and crying, for since they consist almost wholly of muscular exertion, they serve precisely such clarifying purposes as would be served by the gymnastic exercises of an angry man. As it seems to me, the muscular action of laughter clears the system of the energizing substances which have been mobilized in various parts of the body for the performance of other actions (Figs. 27 to 29). If this be true, the first question that presents itself is, Why is the respiratory system utilized for such a clarifying purpose? Why do we not laugh with our feet and hands as well? Were laughter expressed with the hands, the monkey might fall from the tree and, if by the feet, man might fall to the ground. He would at least be ataxic. In fact, laughter has the great advantage of utilizing a group of powerful muscles which can be readily spared without seriously interfering with the maintenance of posture. Laughter, however, is only one form of muscular action which may consume the fuel thrown into the blood by excitation. That these products of excitation are often consumed by other motor acts than laughter is frequently seen in public meetings when the stamping of feet and the clapping of hands in applause gives relief to the excitation (Fig. 30). Why the noise of laughter? In order that the products of excitation may be quickly and completely consumed, the powerful group of expiratory muscles must have some resistance against which they can exert themselves strongly and at the same time provide for adequate respiratory exchange. The intermittent closure of the epiglottis serves this purpose admirably, just as the horizontal bars afford the resistance against which muscles may be exercised. The facial muscles are not in use for other purposes, hence their contractions will consume a little of the fuel. An audience excited by the words of an impassioned speaker undergoes a body-wide stimulation for action, all of which may be eliminated by laughter or by applause (Fig. 31).
Let us test this hypothesis by some practical examples. The first is an incident that accidentally occurred in our laboratory during experiments on fear which were performed as follows: A keen, snappy fox terrier was completely muzzled by winding a broad strip of adhesive plaster around his jaw so as to include all but the nostrils. When this aggressive little terrier and the rabbit found themselves in close quarters each animal became completely governed by instinct; the rabbit crouched in fear, while the terrier, with all the ancestral assurance of seizing his prey, rushed, upon the rabbit, his muzzle always glancing off and his attack ending in awkward failure.
This experiment was repeated many times and each time provoked the serious-minded scientific visitors who witnessed it to laughter. Why? Because the spectacle of a savage little terrier rushing upon an innocent rabbit as if to mangle it integrated the body of the onlooker with a strong desire to exert muscular action to prevent the cruelty. This integration caused a conversion of the potential energy in the brain-cells into kinetic energy, and there resulted a discharge into the blood-stream of activating internal secretions for the purpose of producing muscular action. Instantly and unexpectedly the danger passed and the preparation for muscular action intended for use in the protection of the rabbit was not needed. This fuel was consumed by the neutral muscular action of laughter, which thus afforded relief.
A common example of the same nature is that encountered on the street when a pedestrian slips on a banana peel and, just as he is about to tumble, recovers his equilibrium. The onlookers secure relief from the integration to run to his rescue by laughing. On the other hand, should the same pedestrian fall and fracture his skull the motor integration of the onlookers would be consumed by rendering physical assistance—hence there would be no laughter. In children almost any unexpected phenomenon, such as a sudden "booing" from behind a door, is attended by laughter, and in like manner the kinetic reaction produced by the innumerable threats of danger which are suddenly averted, a breach of the conventions, a sudden relief from acute nervous tension; a surprise—indeed, any excitant to which there is no predetermined method of giving a physical response— may be neutralized by the excitation of the mechanism of laughter.
In the same way the laughter excited by jokes may be explained. An analysis of a joke shows that it is composed of two parts— the first, in which is presented a subject that acts as a stimulus to action, and the second, in which the story turns suddenly so that the stimulus to action is unexpectedly withdrawn. The subject matter of the joke affects each hearer according to the type of stimuli that commonly excites that individual. Hence it is that a joke may convulse one person while it bores another, and so there are jokes of the classes, bankers' jokes, politicians' jokes, the jokes of professional men, of the plebeian, of the artist, etc. If the joke fails, the integration products of the excitation may be used in physical resentment (Fig. 32).
Another type of laughter is that associated with the ticklish points of certain parts of the body, the soles of the feet and certain parts of the trunk and of the abdomen. The excitation of the ticklish receptors, like pain, compels self-defensive motor acts. This response is of phylogenetic origin, and may be awakened only by stimuli which are too light to be painful. In this connection it is of interest to note that a superficial, insect-like contact with the skin rarely provokes laughter, and that the tickling of the nasal, oral, and pulmonary tracts does not produce laughter. The ticklish points that cause laughter are rather deeply placed, and a certain type of physical contact is required to constitute an adequate stimulus. That is, the contact must arouse a phylogenetic association with a physical struggle or with physical exertion. In the foot, the adequate stimuli for laughter are such contacts as resemble or suggest piercing by stones or rough objects.. The intention of the one who tickles must be known; if his intention be playful, laughter results, whereas if injury be intended, then an effort toward escape or defense is excited, but no laughter. If deep tickling of the ribs is known to be malicious, it will excite physical resentment and not laughter. Self-tickling rarely causes laughter for the reason that auto-tickling can cause only a known degree of stimulation, so that there results no excessive integration which requires relief by the neutral muscular activity of laughter. In fact, one never sees purposeful acts and laughter associated. According to its severity, an isolated stimulus causes either an action or laughter. The ticklish points in our bodies were probably developed as a means of defense against serious attacks and of escape from injurious contacts.
Anger, fear, and grief are also strong excitants and, therefore, are stimuli to motor activity. It is obvious that whatever the excitant the physico-chemical action of the brain and the ductless glands cannot be reversed—the effect of the stimulus cannot be recalled, therefore either a purposeful muscular act or a neutralizing act must be performed or else the liberated energy must smoulder in the various parts of the body.
It is on this hypothesis that the origin and the purpose of laughter and crying may be understood. Even a superficial analysis of the phenomena of both laughter and crying show them to be without any external motor purpose; the respiratory mechanism is intermittently stimulated and inhibited; and the shoulder and arm muscles, indeed, many muscles of the trunk and the extremities are, as far as any external design is concerned, purposelessly contracted and released until the kinetic energy mobilized by excitation is utilized. During this time the facial expression gives the index to the mental state.
Crying, like laughter, is always preceded by a stimulation to some motor action which may or may not be performed (Figs. 33 and 34). If a mother is anxiously watching the course of a serious illness of her child and if, in caring for it, she is stimulated to the utmost to perform motor acts, she will continue in a state of motor tenseness until the child recovers or dies. If relief is sudden, as in the crisis of pneumonia, and the mother is not exhausted, she will easily laugh if tired, she may cry. If death occurs, the stimulus to motor acts is suddenly withdrawn and she then cries aloud, and performs many motor acts as a result of the intense stimulation to motor activity which is no longer needed in the physical care of her child. With this clue we can find the explanation of many phenomena. We can understand why laughter and crying are so frequently interchangeable; why they often blend and why either gives a sense of relief; we can understand why either laughter or crying can come only when the issue that causes the integration is determined; we can understand the extraordinary tendency to laughter that discloses the unspoken sentiments of love; we can understand the tears of the woman when she receives a proposal of marriage from the man she loves; we can understand why any averted circumstance, such as a threatened breach of the conventions, which would have led to embarrassment or humiliation, leads to a tendency to laughter; and why the recital of heroic deeds by association leads to tears, On the other hand, under the domination of acute diseases, of acute fear, or of great exhaustion, there is usually neither laughter nor crying because the nervous system is under the control of a dominating influence as a result of which the body is so exhausted that the excess of energy which alone can produce laughing or crying is lacking.
A remarkable study of the modification of laughter and crying by disease is found in that most interesting of diseases—exophthalmic goiter. In this disease there is a low threshold to all stimuli. That the very motor mechanism of which we have been speaking is involved, is shown by an enormous increase in its activity. There is also an increase in the size of certain at least of the activating glands—the thyroid and the adrenals are enlarged and overactive and the glycogen-producing function of the liver is stimulated. The most striking phenomenon of this disease, however, is the remarkable lowering of the brain thresholds to stimuli. In other words, in Graves' disease the nervous system and the activating glands— the entire motor mechanism—are in an exalted state of activity.
If this be true, then these patients should exhibit behavior precisely contrary to that of those suffering from acute infection, that is, they should be constantly clearing their systems of these superabundant energizing materials by crying or laughing, and this is precisely what happens—the flood-gates of tears are open much of the time in Graves' disease—a disease of the emotions.
We have already interpreted pain as a phenomenon of motor activity. When pain does not lead to muscular activity it therefore frequently leads to crying or to moaning, just as tickling, which is equally an incentive to motor activity, results in laughter if it does not find full expression in action.
From the foregoing we infer that pain, the intense motor response to tickling, and emotional excitation are all primitive biologic reactions for the good of the individual, and that all have their origin in the operation of the great laws of evolution. If to this inference we add the physiologic dictum that the nervous system always acts as a whole, and that it can respond to but one stimulus at a time, we can easily understand that while diverse causes may integrate the nervous system for a specific action, if the cause be suddenly removed, then the result of the integration of the nervous system may be, not a specific action, but an undesigned muscular action, such as crying or laughter. Hence it is that laughter and crying may be evoked by diverse exciting causes. The intensity of the laughter or of the crying depends upon the intensity of the stimulus and the dynamic state of the individual.
The linking together of these apparently widely separated phenomena by the simple law of the discharge of energy by association perhaps explains the association of an abnormal tendency to tears with an abnormally low threshold for pain (Fig. 36). In the neurasthenic, tears and pain are produced with abnormal facility. Hence it is that, if a patient about to undergo a surgical operation is in a state of fear and dread before the operation, the threshold to all stimuli is lowered, and this lowered threshold will continue throughout the operation, even under inhalation anesthesia, because the stimulus produced by cutting sensitive tissue is transmitted to the brain just as readily as if the patient were not anesthetized. In like manner, the brain may be sensitized by the administration of large doses of thyroid extract prior to operation, the threshold to injury in such a case continuing to be low to traumatic stimuli even under anesthesia. Under the sensitizing influences of thyroid extract or of Graves' disease the effect of an injury, of an operation, or of emotional excitation is heightened. The extent to which the threshold to pain or to any other excitant is affected by Graves' disease is illustrated by the almost fatal reaction which I once saw result from the mere pricking with a hypodermic needle of a patient with this disease. As the result of a visit from a friend, the pulse-rate of a victim of this disease may increase twenty beats and his temperature rise markedly. I have seen the mere suggestion of an operation produce collapse. As the brain is thus remarkably sensitized in Graves' disease, we find that in these patients laughter, crying, emotional disturbances, and surgical shock are produced with remarkable facility.
I hope that even this admittedly crude and imperfect consideration of this subject will suggest the possibility of establishing a practical viewpoint as to the origin and purpose of pain, of tickling, and of such expressions of emotion as laughter and crying, and that it may help us to understand their significance in health and in disease.
THE RELATION BETWEEN THE PHYSICAL STATE OF THE BRAIN-CELLS AND BRAIN FUNCTIONS—EXPERIMENTAL AND CLINICAL[*]
[*] Address before The American Philosophical Society, April 18, 1913.
The brain in all animals (including man) is but the clearing-house for reactions to environment, for animals are essentially motor or neuromotor mechanisms, composed of many parts, it is true, but integrated by the nervous system. Throughout the phylogenetic history of the race the stimuli of environment have driven this mechanism, whose seat of power—the battery—is the brain.
Since all normal life depends upon the response of the brain to the daily stimuli, we should expect in health, as well as in disease, to find modifications of the functions and the physical state of the component parts of this central battery— the brain-cells. Although we must believe, then, that every reaction to stimuli, however slight, produces a corresponding change in the brain-cells, yet there are certain normal, that is, non-diseased, conditions which produce especially striking changes. The cell changes due to the emotions, for example, are so similar, and in extreme conditions approach so closely to the changes produced by disease, that it is impossible to say where the normal ceases and the abnormal begins.
In view of the similarity of brain-cell changes it is not strange that in the clinic as well as in daily life, we are confronted constantly by outward manifestations which are so nearly identical that the true underlying cause of the condition in any individual case is too often overlooked or misunderstood. In our laboratory experiments and in our clinical observations we have found that exhaustion produced by intense emotion, prolonged physical exertion, insomnia, intense fear, certain toxemias, hemorrhage, and the condition commonly denominated surgical shock, produce similar outward manifestations and identical brain-cell changes.
It is, therefore, the purpose of this paper to present the definite results of laboratory researches which show certain relations between alterations in brain functions and physical changes in the brain-cells.
Fear.—Our experiments have shown that the brain-cell changes due to fear may be divided into two stages: First, that of hyperchromatism— stimulation; second, that of hypochromatism—exhaustion (Figs. 5 and 13). Hyperchromatism was shown only in the presence of the activating stimuli or within a very short time after they had been received. This state gradually changed until the period of maximum exhaustion was reached—about six hours later. Then a process of reconstruction began and continued until the normal state was again reached.
Fatigue.—Fatigue from overexertion produced in the brain-cells like changes to those produced by fear, these changes being proportional to the amount of exertion (Fig. 4). In the extreme stage of exhaustion from this cause we found that the total quantity of Nissl substance was enormously reduced. When the exertion was too greatly prolonged, it took weeks or months for the cells to be restored to their normal condition. We have proved, therefore, that in exhaustion resulting from emotion or from physical work a certain number of the brain-cells are permanently lost. This is the probable explanation of the fact that an athlete or a race-horse trained to the point of highest efficiency can reach his maximum record but once in his life. Under certain conditions, however, it is possible that, though some chromatin is forever lost, the remainder may be so remarkably developed that for a time at least it will compensate for that which is gone.
Hemorrhage.—The loss of blood from any cause, if sufficient to reduce the blood-pressure, will occasion a change in the brain-cells, provided that the period of hypotension lasts for more than five minutes. This time limit is a safeguard against permanent injury from the temporary hypotension which causes one to faint. If the hemorrhage be long continued and the blood-pressure be low, there will be a permanent loss of some of the brain-cells. This explains why an individual who has suffered from a prolonged hemorrhage will never again be restored to his original powers.
Drugs.—According to their effect upon the brain-cells, drugs may be divided into three classes: First, those that stimulate the brain-cells to increased activity, as strychnin (Fig. 37); second, those that chemically destroy the brain-cells, as alcohol and iodoform (Figs. 38 and 39); third, those that suspend the functions of the cells without damaging them, as nitrous oxid, ether, morphin. Our experiments have shown that the brain-cell changes induced by drugs of the first class are precisely the same as the cycle of changes produced by the emotions and by physical activity. We have found that strychnin, according to the dosage, causes convulsions ending in exhaustion and death; excitation followed by lassitude; stimulation without notable after-results; or
{illust. caption = A, Section of Cerebellum of Normal Dog. C, Section of Cerebellum of Dog after Repeated Doses of Strychnin. FIG. 37.— BRAIN-CELLS SHOWING STAGE OF HYPERCHROMATISM FOLLOWED BY CHROMATOLYSIS RESULTING FROM THE CONTINUATION OF THE STIMULUS. (Camera lucida drawings.)increased mental tone; while the brain-cells accurately display these physiologic alterations in proportional hyperchromatism in the active stages, and proportional chromatolysis in the stages of reaction. The biologic and therapeutic application of this fact is as obvious as it is important.
In our experiments, alcohol in large and repeated dosage caused marked morphologic changes in the brain-cells which went as far even as the destruction of some of the cells (Fig. 39). Ether, on the other hand, even after five hours of administration, produced no observable destructive changes in the brain-cells.
The effect of iodoform was peculiarly interesting, as it was the only drug that produced a rise of temperature. Its observed effect upon the brain-cells was that of wide-spread destruction.
Infections.—In every observation regarding the effect of pyogenic infections on dogs and on man we found that they caused definite and demonstrable lesions in certain cells of the nervous system, the most marked changes being in the cortex and the cerebellum (Fig. 40). For example, in fatal infections resulting from bowel obstruction, in peritonitis, and in osteomyelitis, the real lesion is in the brain-cells. We may, therefore, reasonably conclude that the lassitude, the diminished mental power, the excitability, irritability, restlessness, delirium, and unconsciousness which may be associated with acute infections, are due to physical changes in the brain-cells.
Graves' Disease.—In Graves' disease the brain-cells show marked changes which are apparently the same as those produced by overwork, by the emotions, and by strychnin. In the postmortem examination of one advanced case it was found that a large number of brain-cells were disintegrated beyond the power of recuperation, even had the patient lived. This is undoubtedly the reason why a severe case of exophthalmic goiter sustains a permanent loss of brain power.
Insomnia.—The brains of rabbits which had been kept awake for one hundred hours showed precisely the same changes as those shown in physical fatigue, strychnin poisoning, and exhaustion from emotional stimulation. Eight hours of continuous sleep restored all the cells except those that had been completely exhausted. This will explain the permanent ill effect of long-continued insomnia; that is, long-continued insomnia permanently destroys a part of the brain-cells just as do too great physical exertion, certain drugs, emotional strain, exophthalmic goiter, and hemorrhage. We found, however, that if, instead of natural sleep, the rabbits were placed for the same number of hours under nitrous oxid anesthesia, not only did the brain-cells recover from the physical deterioration, but that 90 per cent. of them became hyperchromatic. This gives us a possible clue to the actual chemical effect of sleep. For since nitrous oxid owes its anesthetic effect to its influence upon oxidation, we may infer that sleep also retards the oxidation of the cell contents. If this be true, then it is probable that inhalation anesthetics exert their peculiar influence upon that portion of the brain through which sleep itself is produced. If nitrous oxid anesthesia and sleep are chemically identical, then we have a further clue to one of the primary mechanisms of life itself; and as a practical corollary one might be able to produce artificial sleep which would closely resemble normal sleep, but which would have this advantage, that by using an anesthetic which interferes with oxidation the brain-cells might be reconstructed after physical fatigue, after emotional strain, or after the depression of disease.