But even in such a case the essential preliminary condition is always the recognition of the internal causes which have given rise to the disease in question.

The important question here is the differentiation of the root causes from the circumstances developing out of them. This becomes all the more difficult the longer the germs of disease remain in the national body and the longer they are allowed to become an integral part of that body. It may easily happen that, as time goes on, it will become so difficult to recognize certain definite virulent poisons as such that they are accepted as belonging to the national being; or they are merely tolerated as a necessary evil, so that drastic attempts to locate those alien germs are not held to be necessary.