The law of natural selection will continue to work on them so long as its action is required, with little regard to the efforts of man to abrogate it. Nature works continuously for ages, and she works on every part of man, every organ, every function. We may almost say she is omnipotent; that she watches for every slight improvement; that she knows what to do under every circumstance. Foiled in one direction, she has other means, infinite means, for gaining her ends. Man can no more put a stop to the operation of natural law than he can put a stop to the flow of Niagara. He may turn off a trifle of its water to whirl wheels and spindles, but the mighty river flows on until nature makes some changes in the watersheds, that make its flow impossible. Man, on the other hand, acts on his own body in a finite way. He works mainly for immediate, not remote, ends. He changes his methods as his needs change, or his knowledge increases. Today he works with limited knowledge of hygiene, inspired by old ideas of philanthropy. Tomorrow he may have a vastly extended knowledge of this subject and an entirely new social science which will enable him to do more good and less harm. IDEAL OF HEALTH.--Let me now consider some of the things necessary to give us a greater hope for the future of human health, of ourselves and for our children. The first thing necessary is to get a higher ideal of bodily or physical perfection than we have today. Sir James Paget, in a lecture on National Health, in 1884, put this in the following words: "We want," says he, "more ambition for health. _I should like to see a personal ambition for health as keen as that for bravery, for beauty, or for success in our athletic games or field sports. I wish there was such an ambition for the most perfect national health as there is for national renown in war, in art or in commerce._" Sir James then gives his own ideal. It is for man or woman to be so full of health as to be comparatively indifferent to the external conditions of life, and to make a ready self-adjustment to all its changes. He should not be deemed thoroughly healthy who is made better or worse, more fit or less fit, by every change of weather or food, or who is bound to observe exact rules of living. It is good to observe rules, and to some they are absolutely necessary; but it is better to need none but those of moderation, and, observing these, to be willing to live and work hard in the widest variations of food, air, climate, bathing and all other sustenances of life. ADAPTATION TO ENVIRONMENT.--This sounds very much like saying that to be healthy one must be adjusted to his environment; and this is practically what Herbert Spencer long before said in his "Principles of Biology." Here are his words: