This, is indeed, the definite purpose of my discourse; to point out that civilized man has proceeded so far in his interference with extra-human nature, has produced for himself and the living organisms associated with him such a special state of things by his rebellion against natural selection and his defiance of Nature’s pre-human dispositions, that he must either go on and acquire firmer control of the conditions or perish miserably by the vengeance certain to fall on the half-hearted meddler in great affairs. We may indeed compare civilized man to a successful rebel against Nature who by every step forward renders himself liable to greater and greater penalties, and so cannot afford to pause or fail in one single step. Or again we may think of him as the heir to a vast and magnificent kingdom who has been finally educated so as to fit him to take possession of his property, and is at length left alone to do his best; he has wilfully abrogated, in many important respects, the laws of his mother Nature by which the kingdom was hitherto governed; he has gained some power and advantage by so doing, but is threatened on every hand by dangers and disasters hitherto restrained: no retreat is possible--his only hope is to control, as he knows that he can, the sources of these dangers and disasters. They already make him wince: how long will he sit listening to the fairy-tales of his boyhood and shrink from manhood’s task? A brief consideration of well-ascertained facts is sufficient to show that Man, whilst emancipating himself from the destructive methods of natural selection, has accumulated a new series of dangers and difficulties with which he must incessantly contend. 14. MAN AND DISEASE.