Further, the temporary condition known as exhaustion enters into the relation. Limbs overworn by prolonged exertion, cannot without aching perform acts which would at other times cause no appreciable feeling. After reading continuously for very many hours, even strong eyes begin to smart. And noises that can be listened to for a short time with indifference, become, if there is no cessation, causes of suffering. So that though there is absoluteness in the relation between positive pains and actions that are positively injurious, in so far that wherever there is sentiency it exists; yet even here partial relativity may be asserted. For there is no fixed relation between the acting force and the produced feeling. The amount of feeling varies with the size of the organism, with the character of its outer structures, with the character of its nervous system; and also with the temporary states of the part affected, of the body at large, and of the nervous centers. § 65. The relativity of pleasures is far more conspicuous; and the illustrations of it furnished by the sentient world at large are innumerable. It needs but to glance round at the various things which different creatures are prompted by their desires to eat and are gratified in eating--flesh for predaceous animals, grass for the herbivora, worms for the mole, flies for the swallow, seeds for the finch, honey for the bee, a decaying carcass for the maggot--to be reminded that the tastes for foods are relative to the structures of the creatures. And this truth, made conspicuous by a survey of animals in general, is forced on our attention even by a survey of different races of men. Here human flesh is abhorred, and there regarded as the greatest delicacy; in this country roots are allowed to putrefy before they are eaten, and in that the taint of decay produces disgust: the whale's blubber which one race devours with avidity, will in another by its very odor produce nausea. Nay, without looking abroad we may, in the common saying that "one man's meat is another man's poison," see the general admission that members of the same society so far differ, that a taste which is to these pleasurable is to those displeasurable. So is it with the other senses. Assafoetida, which by us is singled out as typical of the disgusting in odor, ranks among the Esthonians as a favorite perfume, and even those around us vary so far in their likings that the scents of flowers grateful to some are repugnant to others. Analogous differences, in the preferences for colors, we daily hear expressed. And in a greater or less degree the like holds with all sensations down even to those of touch: the feeling yielded by velvet, which is to most agreeable, setting the teeth on edge in some.