If the science of' man appeared as an extension of the science of life, it is because it was medically, as well as biologically, based: by transference, importation, and, often, metaphor, the science of man no doubt used concepts formed by biologists; but the very subjects that it devoted itself to (man, his behaviour, his individual and social realizations) therefore opened up a field that was divided up according to the principles of the normal and the pathological.