Suppose now we drop the dubious term “unimpeded”--retaining Hamilton’s idea of “overstrained or repressed exertion” as the condition of pain--and at the same time passing to a physical point of view, mean by “activity” the activity of an _organ_. We thus reach what is substantially Mr. Spencer’s doctrine, that pains are the psychical concomitants of excessive or deficient actions of organs, while pleasures are the concomitants of medium activities.[139] In considering this theory it will be convenient to take pains and pleasures separately: as it is obviously based primarily on experiences of pain rather than of pleasure,--especially of the pains of sense to which Hamilton’s theory seemed palpably inapplicable. Instances are abundant in which pain is obviously caused by excessive stimulation of nerves. Thus when we gradually increase the intensity of sensible heat, pressure, muscular effort, we encounter pain at a certain point of the increase; “deafening” sounds are highly disagreeable; and to confront a tropical sun with unprotected eyeballs would soon become torture. Some pains, again, as Spencer points out, arise from the excessive actions of organs whose normal actions yield no feelings: as when the digestive apparatus is overtaxed. Still in none of these cases does it seem clear that pain supervenes through a mere intensification _in degree_ of the action of the organ in question; and not rather through some change in the kind of action--some inchoate disintegration or disorganisation. And this latter cause--rather than mere quantity of stimulation--is strongly suggested by a consideration of the pains due to wounds and diseases, and even of the transient digestive discomforts which arise from an improper kind rather than an improper quantity of food. And a similar explanation seems to me most probable in the case of pains which, according to Mr. Spencer, arise from “deficient” action. He speaks of these as “discomforts or cravings”; but, as I have before pointed out,[140] bodily appetites and other desires may be strongly-felt impulses to action without being appreciably painful: and, in my experience, when they become decidedly painful, some disturbance tending to derangement may be presumed either in the organ primarily concerned or in the organism as a whole. Thus hunger, in my experience, may be extremely keen without being appreciably painful: and when I find it painful, experience leads me to expect a temporarily reduced power of assimilation, indicating some disorganisation in the digestive apparatus.[141]