If we inquire a little further into the circumstances under which various kinds of pain occur, we gain some fresh suggestions. Among the neuralgias, those are the most acutely agonizing which occur under circumstances of impaired nutrition incident to the period of bodily decay, and strong reasons will be hereafter adduced for the belief that there is especial impairment of the nutrition of the central end of the painful nerves. To find a parallel to the severity of this kind of pains we must turn to the case of organic tumors, which, from their position, structure, and mode of growth, necessarily exercise continuous and severe pressure on the branches or the trunk of a nerve; or to the class of pains which attend severe cramp, or tonic contraction of muscles. Now, it can scarcely be doubted that in the latter instance there is an abnormally rapid and violent destruction of tissue going on; at the very least there is an extraordinarily violent and irregular manifestation of motor force. In any case the patent fact here is dynamic perturbation of a severe kind; and, in the instance of organic tumors exercising steady and continuously increasing pressure on nerves, one can scarcely doubt that a similar perturbation, less intense but more enduring, is necessarily set up. That which can be done in the way of producing severe pain by these severe affections of the peripheral portions of nerves, or of tissues lying outside them, we might _a priori_ expect would be effected by slighter but continuous changes in the nutrition of the more important portion of the nerve itself--its central gray nucleus. One would say that a pathological process which continuously and progressively lowered the standard of nutrition here must interfere from hour to hour, certainly from day to day, with that regular and equable distribution of force which is the essence of unimpeded function. Take, again, the case of the very severe pain which frequently attends inflammation of the pleura and of the peritoneum. Whatever theory of the causation of these pains we may adopt, it is certain that one most important element in their production and maintenance is the continual movement and friction of the affected parts. But there is little doubt that the moving muscles are involved in the inflammatory process, as Dr. Inman has correctly observed. It would seem plain that under these circumstances--an inflamed muscular structure forced to perform its ordinary contractions as well as it can--there must be powerful dynamic perturbation going on.