portant the methods of immunology are, for here we have a disease which, as the result of the application of such methods, is definitely placed among the transmissible diseases and is given a satisfactory theory for prophylaxis in spite of an utter absence of knowledge concerning its causal agent. An analogy is seen in yellow fever, the microorganism causing which we do not know and for which we have no specific treatment, but which is controlled simply through our knowledge of its transmission by the mosquito.
While on the subject of Flexner and his work mention must be made of the most important contribution in recent years to our list of curative sera, the antimeningococcus serum. The production of this serum, which in the best form is the result of the labors of Flexner and his associates, is an accomplishment which, in reducing enormously the mortality of epidemic meningitis, is in itself a sufficient justification for the establishment of the Rockefeller Institute. The beneficial results of its use are very definite and the mode of its administration, by direct injection into the spinal canal, has been of great value in emphasizing the importance of the local treatment of localized infections.
Many other phases of activity in the field of immunity might be presented, but this brief and disconnected summary will, I hope, suffice to indicate something of actual accomplishment in this field, the main lines of present endeavor, and the many opportunities for future achievement. Much of present-day effort may not lead immediately to tangible results—an outcome not uncommon in medical research—but the volume of work in progress and the vigor with which it is being prosecuted promises ultimately the solution of the many problems of the infectious diseases.
The Investigation of Cancer.—In no field of medical science has the modern experimental method given greater results in a few brief years and offered greater promise for the future than in the study of that fatal and obscure disease, cancer. Owing to the brilliant initiative of Jensen in Denmark and Leo Loeb in this country, it has been shown that a form of cancer occurs in certain lower animals, particularly in rats and mice, that can be artificially transmitted from one animal to another of the same species. This fact has afforded a means of studying in detail the method by which a malignant tumor grows in the body and more particularly has thrown light on the resistance or immunity to tumor growth which may occur naturally in certain individuals and which may even be artificially produced. Scattered over the world are small groups of individuals, more particularly in England, in Germany and in America, who are devoting their entire energies to the solution of this problem. From several divergent sources have come published results of experiments which offer the greatest promise that we may soon learn a method of curing these tumors. Already Ehrlich
