Before discussing any of these subjects let us offer here just a word of caution to the enthusiast. The results gained in one field of science cannot be transferred _in toto_ to another field and there be found to fit. Biology has learned much from Physics and Chemistry, but the biological applications of the laws of these sciences must be carried out with the greatest care. Such transference has often been premature and attended by results retardative to progress in the field of Biology. Any formula borrowed from one science and applied in another must be rigorously tested under the new conditions. The indiscriminating application of biological laws in the field of sociology may result in confusion and retardation in the progress of both sciences, or at any rate in their practical applications. As Thomson points out in writing on this topic, human society is not only a complex of individual activities of a strictly biological character, but also and further it involves an integration and regulation of those activities which are not yet, at least, susceptible of concrete biological analysis. Thomson says: "The biological ideal of a healthful, self-sustaining, evolving human breed is as fundamental as the social ideal of a harmoniously integrated society is supreme." The great danger here lies in forgetting the fundamental and general character of the biological principles. The ideals of biology and sociology need not coincide, often they do not, but they must not conflict. In practice Eugenics must be largely a social matter; but in its theory, its fundamentals, it must be largely biological. The coming together of biology and sociology, and their common search for guiding principles in their common endeavor is likely to have results of several kinds. It is likely to bring out more clearly than has yet been done the distinction, in human life and society, between that which is fundamentally biological or animal, and that which is distinctly social. Such information will prove of especial value later when the time comes for the suggestion and carrying out of a definite eugenic program, when the time comes for the real eugenic organization of society. And further the close _rapprochement_ of the two subjects will doubtless result in mutual aid and suggestion in the development of each subject in its own stricter field, outside the limits of their common meeting ground.