II.
The modifications of the organism which accompany physical pain have been so often described that it is enough to trace a slight outline of them. They may be reduced to a single formula: pain is associated with diminution and disorganisation of the vital functions.
1. It acts on the movements of the heart, generally decreasing its frequency; in extreme cases the slackening may go so far as to produce syncope. In animals submitted for experiment in the laboratory, even after removal of the encephalon, painful impressions diminish the cardiac contractions. In man, though the frequency of the pulse is sometimes increased in one form or another, there is always a modification of the rhythm appreciable by the sphygmograph. Bichat was right when he said: “If you wish to know whether pain is real, examine the pulse.”
2. The influence on respiration is more irregular and more unstable; the rhythm becomes abnormal, sometimes rapid, sometimes slow; the inspirations are successively short and deep. But the final result is a notable diminution in the carbonic acid exhaled—that is to say a real slackening of combustion. The temperature is lowered. “I had imagined,” says Mantegazza, “that pain would be accompanied by an increase of heat, muscular action being very intense under the influence of great suffering. Experiment on animals and on myself proved the contrary.”[[17]] Heidenhain and Mantegazza have in fact noted an average diminution of two degrees centigrade, which, according to the latter, may last an hour and a half or more; it would be due to the contraction of the peripheral blood-vessels.
3. The action of pain on digestion is well known, and shows itself by retardation or disturbance: loss of appetite, arrest of secretions, indigestion, vomiting, diarrhœa, etc. If permanent it acts on the general nutrition, and shows itself in modifications of the urinary secretion, and lasting discoloration of the skin or hair. It is not infrequent to find blanching of the hair, the beard or eyebrows in a few days under the influence of great pain.[[18]]
4. The motor functions translate pain in two opposite ways: the passive form of depression, arrest, or total suppression of movements, in which the patient seems overcome; the active form, marked by agitation, contortions, convulsions, and cries. The latter case seems to contradict the general formula connecting pain with diminished activity, and seems to me to have been misinterpreted by some authors. This violent excitement, indeed, is an expenditure which quickly makes itself felt and soon leaves the individual enfeebled. It does not flow, as in joy or play, from a surplus of activity; it is weakening, irregular and spasmodic. It seems to me to originate in the instinctive expression of the emotions. The wounded animal shakes the painful part of his body, his paw or his head, as if trying to expel the suffering. All these disorderly and violent motor reactions are a defence of the organism, a useless and often hurtful defence, but resulting from acts which, formerly or under other circumstances, were adapted to their end.
Lehmann experimented on five persons, submitting them in turn to agreeable and disagreeable impressions, in both cases registering the changes in respiration and in the volume of the arm with the help of Mosso’s plethysmograph.[[19]] His experiments led him to the following conclusions:—
Every agreeable impression produces an increase in the volume of the arm and in the height of the pulse, with increased depth of the respiratory cavity.
A disagreeable impression, when weak, immediately produces a diminution in the volume of the arm and the height of the pulse; but almost at once the volume begins to increase, notwithstanding the diminished pulse, and usually passes beyond its normal state, even when the pulse has returned to its first condition. If the impression is strong but not painful these changes are accentuated, and from the first are accompanied by deep inspirations. Finally, if the impression is painful, not only considerable changes of volume, but powerful respiratory movements and disturbance of the voluntary muscles are produced.
Disagreeable stimulation produces at first a spasm of the superficial vessels, relaxation of the deep vessels, and decreased fulness of the heart’s contractions. The first two factors together produce a sudden and strong diminution in the volume of the limbs. The last two factors together produce a diminished height of pulse, and in consequence of the enfeebled cardiac contractions there is a stasis of the venous blood showing itself in the increased volume of the limb.
These bodily modifications, of which I have summarised the chief features, are commonly regarded as the effects of pain, and this opinion seems even to be accepted in many works on psychology. The opinion cannot, however, be accepted. Pain considered as a psychic event, an internal fact, a pure state of consciousness, is not a cause but a symptom. The cause is the stimulation (of whatever nature) which, coming from the exterior environment, acts on the external senses, or coming from the interior environment, acts on the organic life. It is shown in two ways: on the one hand in the state of consciousness which we call pain, on the other by the physical phenomena above enumerated. The consciousness expresses in one way what the organism expresses in another way. This is not a mere opinion, for experiment shows that circulatory, respiratory, and motor modifications are produced when consciousness is probably defective. Mantegazza has shown that if an intact animal is subjected to pricks, cuts, and burns, cardiac troubles follow; but that the same phenomena are produced after the removal of the encephalon. François-Franck, investigating the effects of painful stimulation on the heart, found that the anæsthesia of chloroform suppresses troubles of the heart, while, on the contrary, removal of the cerebral hemispheres fails to abolish them. Formerly, Longet and Vulpian maintained that in animals reduced to the medulla and lower parts of the cerebro-spinal axis the cries and movements that occur when they are pinched are purely reflex; this interpretation has been contested by Brown-Séquard. In human anencephalic (or headless) monsters, cries, movements of suction and the like have been observed during the few days they are able to live. We must then admit either that the state of consciousness we call pain can be produced in the absence of the brain, or else that the physical phenomena can exist alone without their psychic concomitant.
Pain (as a state of consciousness) is only a sign, an index, an internal event revealing to the individual his own disorganisation. The only case in which pain is a cause is when, being firmly fixed in consciousness and completely filling it, it becomes an agent of destruction, but then it is only a secondary cause. That is one of those cases, so frequent in the sciences of life, in which what is primarily an effect becomes in turn a cause. It is therefore an error, though common to most psychologists, to consider pain and pleasure as fundamental elements of the affective life; they are only marks, the foundation is elsewhere. What would be said of a doctor who confused the symptoms of a disease with its essential nature?
We touch here a point so important that it needs emphasis. The thesis that pain is only a symptom, and altogether, in spite of the sovereign part it plays in human life, a superficial phenomenon in relation to the tendencies which lie at the basis of the affective life, finds support in the facts of analgesia, the disappearance of capacity to feel pain. This insensibility presents itself under two forms: spontaneous and artificial.
Spontaneous analgesia is the rule in hysteria; it may vary in degree, position, and extent. The demonologists of the Middle Ages and the Renaissance knew these migrations of insensibility to various parts of the body, and they sought with care for the stigmata diaboli, that is, the regions insensible to pain. Some authors assign to it a purely psychic cause: painful impressions cannot be felt because they are outside the field of consciousness, which in these patients is in an almost permanently disassociated, scattered, and destroyed state.[[20]] It is, on the contrary, certain that an intense fixed idea, profound concentration of attention, fanatical exaltation, can produce temporary or permanent analgesia. Many soldiers, in the heat of battle, have not felt their wounds. Pascal, plunged in his problems, escaped his neuralgias. The Aïssaouas, the fakirs, certain Lamas of Thibet tear and cut themselves, secured against pain by delirium, and one may well believe that many martyrs, in the midst of their torture, have only experienced a sense of rapture. In certain forms of insanity (maniacal excitement, melancholia, idiocy, etc.) this spontaneous analgesia is frequent, and takes on extraordinary forms. Numerous examples may be found in special treatises.[[21]] One crushes glass in his mouth for half-an-hour without feeling any pain. Another breaks his leg in a struggle, and a fragment of the tibia projects through the torn skin, yet he continues to pursue the object of his rage, and then sits down to eat without the least sign of pain on his face. There are many who, intentionally or by accident, plunge their arms into boiling water or place them on a red-hot stove, until the skin falls off in shreds, without appearing to be disturbed. An endless series of such facts might be narrated.[[22]]
The artificial analgesias, produced by chloroform and the various anæsthetics employed in surgical operations, are more instructive. It has been asked if the movements, objurgations, and cries of some patients do not prove that the analgesia is not complete, even when it seems so. Richet has expressed the opinion that it is not consciousness but recollection which is defective; he regards the pain as so rapid that it is only a mathematical movement and leaves no echo behind it, there being a series of evanescent states of consciousness. It is quite possible to maintain this hypothesis; but the most important fact recorded by this author seems to me to be that, when pain has disappeared, a certain degree of knowledge of it remains. In other words, there is a process of scission: the feeling man has disappeared, the intellectual man remains. In many simple operations the contact of the instrument is often felt, but not the pain. But there are more complex cases. "In an operation for fissure of the anus with fistula, the patient felt the contact of the scissors and easily distinguished four incisions; she could not speak, but felt no suffering. In the course of a similar operation I asked the patient, ‘How old are you?’ She replied that she was forty-one, but when restored to consciousness she could recall no sensation of wound or burn and complained that the operation had not taken place. I asked another during the operation, ‘How are you getting on?’ the reply was, ‘Not badly.’ At the same moment I pricked her vigorously; she felt nothing. Again, in another case when I introduced a forceps into the mouth to hold the tongue the patient said, ‘Take away that cigarette.’ On awaking he could remember nothing. Another when a quill was passed beneath his nose said, ‘Do not tickle me’ at the moment when the large arteries were being tied, the most painful part of the operation. Finally, a man under chloroform, while his spermatic cord was being tied, heard the clock strike and tranquilly remarked, ‘Half-past eleven,’ recalling nothing when he awoke."[[23]]
I have quoted these facts to show the extent to which pain, as a state of consciousness, is separable, how it can be added or cast off, and to what extent it presents the character of an epiphenomenon.
This relative independence of the pain-phenomenon, against which the intellectualists have always rebelled,[[24]] seems to me corroborated by the retardation which I have already noted in passing. If we strike a corn while walking, we feel the shock before the pain; the cold of the knife is felt before the pain of the incision. Beau estimates that pain is delayed seven-tenths of a second behind the tactile impression. Burckhardt, by precise investigation, fixes the rapidity of transmission in the cord at 12 m. 9 per second for painful impressions, and 43 m. 3 for the others. In certain diseases like tabes dorsalis the pain may be separated from the needle-prick which causes it by from one to two seconds. Many other facts may be quoted. If a fold of the skin is seized in a pressure forceps, stopping at the moment when the pressure is sufficient, pain, not felt at first, gradually appears, coming in waves, and being at last unbearable. A man whose thumb was seized in a machine only knew of his injury by feeling his arm drawn, and only began to suffer a quarter of an hour afterwards. It has also been remarked that the syncope produced by violent shocks and traumatism does not appear at once; between the accident and the fainting several minutes may elapse.[[25]]
Pain is the result of a sum of impulses. Naunyn has shown that, in tabes, a mechanical stimulus (like a hair on the cutaneous surface of the foot), which is below the threshold of consciousness both as contact and as pain, if repeated from 60 to 600 times a second, is perceived at the end of from six to twenty seconds, and soon becomes an intolerable pain to the patient.
Although excessive sensibility to pain (hyperalgesia) belongs to the pathology of our subject, which will be dealt with in a later chapter, it is necessary to say a few words about it in contrasting it with analgesia, especially in view of the conclusions here reached. This condition is more difficult to observe than insensibility, because here there is only a difference of degree, not the difference between being and not being. But in some cases there is so great a disproportion between the stimulus and the subject’s reaction that we may say without hesitation that sensibility is no longer normal.
It has been observed, in a general manner, that the lower races are not very sensitive to pain. Thus Negroes in Egypt endure, almost without suffering, the most extensive surgical operations (Pruner Bey), and Mantegazza (op. cit., chap. xxvi.) reports a large number of examples. In the peasant sensibility is usually less keen than in the town-dweller, and it may be admitted without hesitation that susceptibility to pain increases with civilisation; what is called stoicism should often be called a feeble degree of sensibility. Hyperalgesia is best seen in cases of extreme nervous over-excitement. In some it is generalised, constituting the “supplicium neuricum,” and the patient says that he is the prey of unspeakable torments. It is less frequent in the case of the special nerves, but is sometimes met. One suffers from the slightest noise, and cannot tolerate the least smell. Pitres quotes the case of a person who shut herself up in a dark room, only coming out at night with a thick shade against the rays of the stars. Those who entered her dark room during the day had to wear sombre clothes, completely concealing the shirt-collar, of which the white reflection was horribly disagreeable to her.[[26]] Cutaneous hyperalgesia is very common, sometimes extending over the whole body, sometimes disseminated in patches. Weir Mitchell, in his book on injuries of the nerves, reports numerous examples; among others, a wounded soldier to whom the mere crumpling of paper caused atrocious pain. Opium-smokers, when they interrupt their habits, feel the least breath of air as icy cold, and complain of intolerable pains in all parts of the body. Hyperalgesia of the deep tissues is also frequent among the hysterical and hypochondriacal.
It must be remarked in passing that just as insensibility to pain (analgesia) is independent of incapacity to receive sensorial impressions (anæsthesia), so hyperalgesia is distinct from hyperæsthesia. The latter is a power of perception much surpassing the average; it is known that certain races and individuals possess extraordinary visual, auditory, or olfactive acuteness; the tactile hyperæsthesia of the blind is also known, and in hypnotised subjects the delicacy of the senses has sometimes seemed miraculous. Hyperalgesia then, like analgesia, shows that pain is relatively independent of the sensations which arouse it.