Strictly speaking, the prophylaxis of interstitial nephritis must include some definite knowledge of the tendencies of the patient to the disease under consideration. This at once opens up a wide field, a large part of which is necessarily speculative or theoretical. Without entering into the speculative field, the pith of this question may be narrowed down for present purposes to the simple interrogatory: Can we predict, with any degree of accuracy, the case or class of cases that, under existing surroundings, will sooner or later develop into or terminate in, interstitial nephritis? If, in our present knowledge, a negative answer to this question is necessary, then the prophylaxis of interstitial nephritis necessarily becomes a myth, for, strictly interpreted, the term has only to do with prevention, and prevention is clearly impossible where we have no definite knowledge of the approach or tendency to disease. If, on the other hand, we