Races, therefore, subject to epidemics of a particular fever, suffer selections in the hands of the microbe of that particular fever, and those living are survivals cast in the most resisting mould. It may not be flattering to our national vanity to look upon Englishmen as the product of the selection of the micro-organisms of measles, scarlet fever, small-pox, etc., but the reasonableness of the conclusion seems to be forced upon us when we consider his immunity from these diseases as compared with that of natives of the interior of Africa, or of the wilds of America, whose races have never been so selected, and who, when attacked for the first time by these diseases, are ravaged almost to extermination. We find, then, that an ordinary attack of measles, scarlet fever, whooping cough, erysipelas, typhoid, or typhus fever, when it has passed away, leaves the tissues of the body in as sound and healthy a condition as before; and, indeed, were it not for this fact, the human race could hardly have existed at all, continually exposed as it has been, for countless ages, to the aggressions of these microbes. By exterminating these diseases, we shall, no doubt, preserve countless lives to the community, who will in their turn become race producers, but, inasmuch as the individuals thus preserved will in many cases belong to the feebler and less resisting of the community, the race will not become more robust. In fact, it is probable that, as a race, we shall thereby suffer, for the banishment of the disease will enable the feebler members of the community to live, and in larger proportion contribute to the progeny of the future. That this is actually the case will shortly be pointed out. _Leprosy an Exterminator of the Unhealthy._ But there are other microbes which, in addition to the production of blood changes, have a profound and lasting effect upon many of the tissues of the body. Such are the microbes of leprosy and syphilis. The terrible ravages that the microbe of leprosy is capable of effecting are appreciated only by those who in Norway or elsewhere have visited those death-houses now fortunately to be found in but one or two parts of Europe. Yet, even in this case, strange to say, the germ cells do not seem to be reached by this loathsome disease, and it is not transmitted from parent to child.[13] A disease of mediæval, not of modern, Europe, we need not discuss its action on racial change more than to say that, hideous as are its aspects, it must be looked upon as a friend to humanity; for, while the microbe of typhoid fever will attack a man who is healthy and living in healthy surroundings--excepting for the microbe that lurks in his well--the microbe of leprosy feeds upon those who are debilitated by conditions under which healthy and strong racial development is impossible. It is a depopulator of starved, ill-nourished districts, and the race recruits to its advantage from those more favourably placed.