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.
III.
We may conclude, from what goes before, that though physical pain (of which alone I am speaking at present) is always bound to an internal or external sensation, and forms part of a psychic complexus, it may be separated and disjoined. It has then its own conditions of existence, and we may, in advance, say as much for pleasure.
What are these conditions of existence? or, more simply, what is pain in its nature? At the present time there are two distinct doctrines on this point: one, which counts few adherents, regards physical pain as properly a sensation; the other, more generally admitted, regards it as a quality of sensation, or more correctly, as an accompaniment, a concomitant.[[27]]
The first, though recent in its complete form, is not without antecedents. It found a momentary support in the supposed discovery of pain-bearing nerves. Nichols, one of the promoters of this hypothesis, has developed it in this direction; but the attempt has proved futile. Strong, one of its warmest partisans, supported himself on other grounds. In his opinion the difficulty arises from the ambiguity of the word pain, which may mean two things—displeasure (Unlust), or physical pain in the positive sense. He reduces the latter to cuts, pricks, burns—in short, to those pains that affect the skin. It is, in his opinion, strictly a sensation like blue or red—not an attribute, but a substantive. The pain of a burn, for instance, is a mixture of two sensations, heat and pain. General sensibility is composed of four kinds of sensibility: touch, heat, cold, and pain. Each can be abolished separately. Cocaine and chloroform suppress pain, not touch; saponine suppresses touch, not pain; syringomyelia destroys sensibility to pain and heat, not touch; in some forms of neuritis there is suppression of touch without analgesia. These various facts are invoked as the chief arguments in favour of the hypothesis of pain-sensation, though they may all be explained also by the other doctrine.