If every able-bodied man in the world today were to be slain, and only the weak and puny left, although the injury would be incalculable and would make the whole race stagger, still the next generation of men would be almost as able-bodied and as fit as the present generation. Let us see why: It is because of that great potentiality--atavism. Children inherit not only directly from their parents, but their inheritance harks back to grandfather, great-grandfather, and even to remote ancestry. Just as a stream of water burdened with impurities is self-purifying when it suns itself on the bright pebbles and on grass and moss that web and tangle it, so life is self-purifying and self-regenerative. Nature is constantly reaching higher and higher. The acquired characteristics of parents tend to become instinctive in their children. Instinct is largely inherited experience. Nature strives to protect herself against degeneracy. Though bad conduct on the part of parents harmfully affects the child, yet such influences are less potent than those that are regenerative. If this were not true, Nature's ends would not be so well secured. There is in all animal organisms a certain innate power of resistance to germs of disease, and there is likewise in man a similar power of resistance to degeneracy. The forces that operate to protect the individual operate also to shield the species by affording protection against evil inheritance. Abnormal types are not always representative of diseased or degenerate conditions; other considerations must be weighed. Even some criminals may be atavic examples of a class of individuals who were better suited to live under the savage conditions that existed many generations ago. Nature has resources for her protection far beyond our ken. Some of them have, by our inquiry, been discovered. We have discovered that not only do we immunize ourselves to withstand repeated attacks from the same disease, but also our children to some extent inherit that immunity. When syphilis, the most abominable disease that ever afflicted mankind, was brought to Europe by the sailors of Columbus, the Europeans, possessing no immunity against it, died by hundreds of thousands. It afflicted equally all classes, from peasant to king. This disease among the West Indian tribes was slow-moving, and comparatively mild; but it became exceedingly virulent, rapid, and almost always fatal, in the blood of the unimmunized people of the Old World. This disease alone has been more harmful to the human race than all the wars of the world since the dawn of human history.