The painfulness of the feelings produced by forces which tend to destroy organic structures, wholly or in part, is of course common to all creatures capable of feeling. We saw it to be inevitable that during evolution there must everywhere be established such connections between external actions and the modes of consciousness they cause, that the injurious ones are accompanied by disagreeable feelings and the beneficial ones by agreeable feelings. Consequently, pressures or strains which tear or bruise, and heats which burn or scald, being in all cases partially or wholly destructive, are in all cases painful. But even here the relativity of the feelings may in one sense be asserted. For the effect of a force of given quantity or intensity varies partly with the size and partly with the structure of the creature exposed to it. The weight which is scarcely felt by a large animal crushes a small one; the blow which breaks the limb of a mouse produces little effect on a horse: the weapon which lacerates a horse leaves a rhinoceros uninjured. And with these differences of injuriousness doubtless go differences of feeling. Merely glancing at the illustrations of this truth furnished by sentient beings in general, let us consider the illustrations mankind furnish. Comparisons of robust laboring men with women or children show us that degrees of mechanical stress which the first bear with impunity, produce on the others injuries and accompanying pains. The blistering of a tender skin by an amount of friction which does not even redden a coarse one, or the bursting of superficial blood-vessels, and consequent discoloration, caused in a person of lax tissues by a blow which leaves in well-toned tissues no trace, will sufficiently exemplify this contrast.