but past experience with troops in camp would indicate that inoculation was an important factor at San Antonio. The question of the value of preventive inoculation is, however, still an open one. So also are other applications of the principles of immunity, as the production of anti-sera for snake-venom, and for the irritant (and perhaps intoxicating) vegetable agent causing hay fever.
I have earlier in this lecture referred to methods of serum diagnosis depending on agglutination or solution of bacteria or on the precipitation of protein. Immunology has recently contributed to medicine another diagnostic method of great value. Its principle is that of complement fixation, the theory of which is too complicated for brief explanation, but the method as applied to syphilis, in the well-known Wassermann test, has since 1906 occupied a most prominent position in the diagnosis and treatment of this disease, and is now accepted as a method of great value in the more obscure cases, and numerous attempts are being made to apply the principle to other diseases.
Another phase of immunological study is that of anaphylaxis, a subject concerning which the professor of pathology in this university is one of the best known authorities. Anaphylaxis, the condition of increased susceptibility dependent on the sensitization of an organism to a foreign protein, is by no means thoroughly understood, but it has thrown light upon immunity from a new angle and has stimulated an enormous amount of investigation. Its utilization in the detection of specific proteins, its apparent explanation of the tuberculin, mallein and similar reactions, the light it has thrown on serum sickness, so-called, and the possibility it offers of explaining diseases characterized by critical phases, have attracted a host of investigators, who see in it the key to many little understood phenomena of disease. As yet the practical results are meager, but the ultimate outcome promises much for medicine.
Another field, and one in which American investigations have been of the greatest importance, is the study of diseases the etiology of which is unknown, but which, it has been supposed, are in some instances due to filtrable or ultramicroscopic viruses. The recent work on poliomyelitis by Flexner and his associates is an example. This disease, appearing irregularly in sporadic and epidemic form, was in the past not definitely grouped among the infectious diseases. All attempts to find a causative microorganism have failed. The workers of the Rockefeller Institute and also certain European investigators have shown that the tissues of the central nervous system contain the virus, and that when the fluids of such tissues are injected into monkeys, typical poliomyelitis results. Moreover, the experimental evidence points to an elimination of the virus through the upper respiratory passages, thus offering a substantial basis for scientific prophylaxis through the proper care of the secretions of the nose and throat. Such investigations show how im-
