I.
On the first point there has been, from antiquity to the present day, an almost universal and very rare agreement between different schools: pleasure has, as its condition, an increased, pain a diminished activity. I employ this vague formula designedly, because it covers all special formulas. Of these it would be idle to enumerate even the chief. At bottom, in language varying according to the era and the doctrine, all authors say the same thing, employing, according to their cast of intellect, a metaphysical, physical (Léon Dumont), physiological, or psychological formula. The intellectualists themselves agree with the others; considering sensibility as a confused form of intelligence, they say that pleasure is a confused judgment of perfection, and pain a confused judgment of imperfection. In short, if each formula is stripped of the variations adapting it to the particular philosophy of each author, there is a common residue, which, in all alike, is the essential.
The history of these variations on the same theme would be monotonous and unprofitable; it is as well, however, to note that, as our own century advances, the theoretic conception of the ancients tends to grow more precise, to rely more on the support of experience and be justified thereby. We have already seen the two formulas—augmentation, diminution—taking definite shape, showing themselves in the objective and observable changes of nutrition, of the secretions, the movements, the circulation, and the breathing.
Féré’s experiments, he says, “agree perfectly, in showing that pleasurable sensations are accompanied by an increase of energy, and disagreeable ones by a diminution. The sensation of pleasure resolves itself, therefore, into a feeling of power, that of displeasure into a feeling of impotence. We have thus reached the material demonstration of the theoretic ideas propounded by Bain, Darwin, Spencer, Dumont, and others.”[[61]] I may remind the reader that Féré has applied his dynamometric researches to all kinds of sensations: to smell, to taste, to vision modified by glasses of the principal colours of the spectrum, red giving a dynamometric pressure of 42, which progressively descends to 20-17 for violet. For auditory sensations, he finds that the dynamic equivalent is in proportion to the amplitude and number of the vibrations. The same results are found to follow motion, the movements of the upper or lower limb exercising a dynamogenic influence on the corresponding member. Still further: an excitation imperceptible to the consciousness, a latent perception, determines a dynamic effect just as much as a conscious impression. Suggested hallucinations, agreeable or the reverse, are equally accompanied by an increase or diminution of pressure on the dynamometer.
If the formula, “diminution of vital energy,” of which we have found that melancholia is an extreme instance, can give rise to no ambiguity, this is not the case with the opposite formula; and certain authors have, for this reason, thought—and rightly so—that it ought to be stated in precise terms. Pleasure corresponds to an increase of activity; but if we understand by this expression a large quantity of work done, the pleasure would result from a diminution of the potential energy of the organism, as Léon Dumont has pointed out—i.e., from an impoverishment, which is contradicted by experience. We must therefore understand this increase of activity in the sense that the work done does not expend more energy than the nutritive actions; or, to employ Grant Allen’s formula, “Pleasure is the concomitant of the healthy action of any or all of the organs or members supplied with afferent cerebro-spinal nerves, to an extent not exceeding the ordinary powers of reparation possessed by the system.”[[62]]
Finally, we must remark that, if every external or internal sensation, whatever its nature, is a transmission of movements coming from without, a new acquisition for the nervous system and the brain, every sensation ought at first to produce at least a momentary increase of energy. Féré, who has foreseen the possibility of this objection, admits in all cases a primary excitement. “If there appear to be cases in which phenomena of depression arise suddenly and subsist by themselves, it is only because they have been insufficiently observed.”[[63]] There would then be a very short phase of increase, immediately masked, according to him, by the phase of diminution. The physiologists, as we have seen, are always inclined to explain pain by intensity of sensation; but, if we take into account its nature, its quality, and the susceptibility of the nervous system to certain modes of motion received, nothing prevents the loss being immediate.
Meynert, in his Psychiatrie, is the only writer who has attempted to advance any nearer to an explanation, and to determine the mechanism which produces pleasure and pain. His hypothesis, in its principal points, is as follows:—
As far as pain is concerned, his theory may be summed up as an arrestive action of two categories of reflex movements, motor and vascular. The painful state is the translation into consciousness of this physiological mechanism.
1. Motor reflexes.—Let us suppose the head of a sleeping child to be slightly tickled. As the child’s sleep is sound, and there is no pain, nothing takes place but a slight withdrawal of the hand. If we suppose a slight prick, there will be few movements, and these limited to a small part of the body. But if we suppose some severe pain, such as the extraction of a tooth, or a burn extending over a large portion of the skin, the result will be prolonged and terrible reflex movements in all parts of the body, which (in our opinion) may be considered as defensive. So much for external facts; what is taking place internally?
We know that vibrations are conducted slowly in the grey matter (twelve times as slowly, according to Helmholtz, as in the white). When an excitation increases, as we have seen, the number of muscular groups set in motion, resistance to transmission increases in the same proportion. “The sensation of pain presupposes a reflex movement and an arrest of nervous conduction in the grey substance of the spinal marrow.” It is this process of inhibition, in varying degrees, which is felt by the consciousness as pain.