Not only, however, are the pains due to violent incident forces, relative to the characters or constitutional qualities of the parts directly affected, but they are relative in equally marked ways, or even in more marked ways, to the characters of the nervous structures. The common assumption is that equal bodily injuries excite equal pains. But this is a mistake. Pulling out a tooth or cutting off a limb, gives to different persons widely different amounts of suffering; not the endurance only, but the feeling to be endured, varies greatly; and the variation largely depends on the degree of nervous development. This is well shown by the great insensibility of idiots--blows, cuts, and extremes of heat and cold, being borne by them with indifference.[H] The relation thus shown in the most marked manner where the development of the central nervous system is abnormally low, is shown in a less marked manner where the development of the central nervous system is normally low; namely, among inferior races of men. Many travelers have commented on the strange callousness shown by savages who have been mangled in battle or by accident; and surgeons in India say that wounds and operations are better borne by natives than by Europeans. Further, there comes the converse fact that among the higher types of men, larger brained and more sensitive to pain than the lower, the most sensitive are those whose nervous developments, as shown by their mental powers, are the highest; part of the evidence being the relative intolerance of disagreeable sensations common among men of genius,[I] and the general irritability characteristic of them. That pain is relative not to structures only, but to their states as well, is also manifest--more manifest indeed. The sensibility of an external part depends on its temperature. Cool it below a certain point and it becomes, as we say, numb; and if by ether spray it is made very cold, it may be cut without any feeling being produced. Conversely, heat the part so that its blood-vessels dilate, and the pain which any injury or irritation causes is greater than usual. How largely the production of pain depends on the condition of the part affected, we see in the extreme tenderness of an inflamed surface--a tenderness such that a slight touch causes shrinking, and such that rays from the fire which ordinarily would be indifferent become intolerable. Similarly with the special senses. A light which eyes that are in good order bear without disagreeable feeling, cannot be borne by inflamed eyes. And beyond the local state, the state of the system as a whole, and the state of the nervous centers, are both factors. Those enfeebled by illness are distressed by noises which those in health bear with equanimity; and men with overwrought brains are irritated in unusual degrees by annoyances, both physical and moral.