We are in the A, B, C class in powers of repair by comparison with the angleworm, the lobster, or the salamander. Yet we are not without gruesome echoes of this lost power of regeneration in that our whole brood of tumors, including the deadly cancer and sarcoma, are due to a strange resumption, on the part of some little knot of our body-cells, of the power of reproducing themselves or the organ in which they are situated, without any regard to the welfare of the rest of the body. Cancer is, in one sense, a throwing off of the allegiance to the body-state and a resumption of amphibian powers of independent growth on the part of certain groups of our body-cells--literally, a "rebellion of the cells." These are but a handful of scores of instances that could be adduced, showing that the majority of the processes upon which we rely in combating disease and preserving life are the result of the hereditary experiences of our cells. Intelligent physicians are receding completely from that curiously warped and jaundiced view which led us to regard heredity chiefly as a factor in the _production_ of disease. It was, perhaps, natural enough, since it was inevitably only its injurious, or, so to speak, malicious, effects which were brought to our attention to be corrected. But, just as in the growth of our ethnic religions it is Evil that is worshiped first as strongest and most aggressive, and the recognition of the greater power of good comes only at a later stage, so it has been in pathology. Not only do we regard heredity as a comparatively small and steadily receding factor in the production of disease, but we fully and frankly recognize it as the strongest and most important single force in its prevention. All our processes of repair, all the reactions of the body against the attack of accident or of disease, are hereditary endowments, worked out with infinite pains and labor through tens of thousands of generations. The utmost that we can do with our drugs and remedies is to appeal to and rouse into action the great healing power of nature, the classic "_Vis medicatrix Naturae_," an incarnation of our past experiences handed down by heredity. Enormously valuable and important as are the services to human welfare, health, and happiness which can be rendered by the destruction of the living external causes of disease and the prevention of contagion, our most permanent and substantial victories are won by appealing to and increasing this long-descended and hard-won power of individual resistance.