So far we have referred only to those distinctive features which serve us in describing the difference between one pain-sensation and another. But there are undoubtedly other differences which seem incapable of analysis and description. This follows from the diffusive nature of organic sensations. The particular sensation which we regard as painful may have its origin in a burn or a wound in a particular part of the skin, or in a diseased condition of the membrane of the stomach or bowels. The specific nature of the experience will therefore be in part determined by the character of this primary sensation. But the disturbance set up by the localised impression tends to involve more or less the whole nervous system, and to overflow the whole organism. The diffused effect on the nervous system may be marked by some peculiarity in the experience. Certainly, the impressions which arise from the changed conditions of the organism as a whole must modify the total experience in an important degree. But these elements are not easily expressed in definite language. They can, as people say, be felt but not described.

Organic pains and pleasures in extreme degrees of intensity reduce to a minimum cognitive process in general. In having a tooth drawn, our consciousness seems to consist in a single thrill of mere sensation. Attention to definite objects ceases: we cannot be said to attend even to the sensation itself, except in the vaguest way. We do not take note of its peculiar qualities, we simply feel it. The distinction between subject and object seems for the moment almost lost. It remains true that the experience has a peculiar quality which might be analysed and described by a demon which had taken possession of us and was watching our mental processes. But no approach to such analysis and description is possible to us until the experience is over, and we can calmly regard it in retrospect.

Pain-Sensations may arise through disintegration of tissue or excessive stimulation in almost any part of the surface of the body. The question arises, how far are they due to the existence of nerves of common sensibility terminating in the skin and other sensitive surfaces, and how far they may be produced by stimulation of the nerves subserving the special senses. It appears probable that stimulation of the nerves of sight and hearing does not result of itself in pain-sensations, strictly so called. But the case of cutaneous impressions is more doubtful. Goldscheider has found that a continued series of taps on a point peculiarly sensitive to pressure may suddenly give rise to a new sensation distinctly different in kind from those of pressure which had previously accompanied the several taps. This new sensation, due to the cumulative effect of repeated impressions, is organic in its nature, and bears the general character of a pain-sensation although it may not be acutely painful. Now the question may be raised whether the same nerveendings which were the medium of the sensation of pressure were also the medium of this other sensation. Again, let us suppose a needlepoint thrust into the skin; at first only a sensation of pressure is felt, which may be more or less disagreeable. It is only after the lapse of an appreciable interval of time that the pain-sensation of pricking occurs. The timeinterval points to the possibility that the pain-sensation and the pressure-sensation, respectively, are subserved by different nerves. This view appears to be reinforced by certain pathological phenomena. There are cases when sensitiveness to temperature and pressure remains intact while pain-sensations are no longer producible. This sometimes happens to patients under chloroform or other anaesthetics. It also occurs in leadpoisoning and in some cases of nervous disease. The inverse also may take place. Susceptibility to pain-sensation may be retained, though pressure and temperature-sensations are no longer producible. These facts seem to show that the nerves of common sensibility and those of special sensations are distinct and separate. But there is one weak point in the argument. The pathological phenomena only occur under conditions which produce abnormal states of the nervous system. We may explain the facts, not by supposing separate and distinct sets of nervefibres terminating in the skin, but by supposing that the effect of the same impression on the same nerve is altered by the altered state of the central nervous matter to which it is conveyed. It has been found that removal or disablement of the grey matter of the spinal cord produces insensibility to pain-sensations, while sensibility to pressure and temperature-sensations is left unaffected so long as the white strands of the cord remain intact. Conversely, cutting through the white strands of the cord destroys sensitiveness to pressure and temperature, but not to pain-sensations. Now before a nervous impulse can be transmitted through grey matter, it must first excite the grey cells so that they discharge in an explosive manner. For this the impulse communicated to them must reach a certain pitch of intensity, and after their discharge the impulse is transmitted in an intensified form. They thus serve as accumulators of nervous energy. In this way we may explain the sudden emergence of a new sensation as the result of a series of successive taps on a pressurepoint. Each tap gives rise to a relatively feeble nervous impulse, which by itself is insufficient to produce a discharge of the grey cells of the cord. But the series of taps by its cumulative effect ultimately succeeds in producing an explosion of the grey matter, and with it a new sensation of an organic character. When the grey matter of the spinal cord is removed, the nervous impulses from the skin, whatever their origin, may fail to produce pain-sensations because they cannot attain the requisite intensity in the absence of an apparatus for accumulation of nervous energy. But there is no reason why they should not still continue to produce pressure and temperature-sensations. Similarly, in the inverse case, all nervous impulses from the skin, in order to produce any sensation at all, must discharge the grey matter of the cord, and in so doing reach a pitch of intensity that can only give rise to pain-sensations. It seems, therefore, very possible that the nerves which subserve temperature and pressure, may also subserve pain-sensations, the difference between the two kinds of experience depending upon more central conditions.