conditions under which certain bacteria can exist, mainly on the basis of more exact studies on the composition of the medium, then we should undoubtedly be in a position to employ more objective therapeutic methods. Further, it would be possible to formulate a conception of the injurious activities of certain kinds of bacteria more clearly than we can at present. Unfortunately, it would scarcely be possible to make use of direct methods in this case, unless we were to succeed in cultivating individual micro-organisms on substrates the composition of which we were thoroughly acquainted with. Our progress in the field of the chemistry of the different kinds of cell units, and of their nutritive bases, has brought us nearer to this objective, but a large part of the road lies before us yet, before we shall obtain such an exact knowledge of the composition of certain albuminous substances, such as phosphatides and nucleoproteids, &c., as to be able to properly appreciate differences of configuration, as well as differences of structure. Once we have advanced so far, we shall be able to replace our present conception of "disposition" by definite facts.
The train of thought we have been pursuing is only intended to show that, in considering the question of the injuries which bacteria may inflict on their host, we must not only consider the bacteria as such, but must realize that their entire metabolism is of
