Page:Popular Science Monthly Volume 81.djvu/121

Rh

HE important activities in scientific medicine at the present time may be said, without fear of contradiction, to be in. the departments of (1) immunology, (2) protozoology, (3) chemotherapy, (4) physiological chemistry, (5) experimental pharmacology and (6) experimental pathology. The methods and problems of these various phases of medicine it is my intention to discuss, some at length, others briefly, in the present lecture.

Immunology is the science which would explain and apply the mechanisms by means of which the animal body is enabled to resist disease. As has been shown, the efforts of bacteriologists until about 1890 were devoted almost entirely to the study of the etiology of the infectious diseases and to attempts to combat these by vaccination with attenuated viruses. Another phase of bacteriology was, however, already under way, and this, in the earlier nineties, not only yielded results of great practical importance, but opened a new and ever-widening field of investigation. This was the study of the mode of action of invading bacteria and their products, that is, of the process of infection and intoxication, and the mechanism by which the host combats the invasion and absorbs or cures such infection by overwhelming the foreign organism. One of the first results was the study of a group of soluble poisons, toxins—formed by certain bacteria and which it has been found are responsible not only for the symptoms which follow certain infections, but also for that effect on the cells of the host which stimulates the formation of the antibodies which we call antitoxins. Pasteur in his study of chicken-cholera had noticed that a bacteria-free filtrate of a culture of the specific microorganism of this disease could cause the symptoms produced by the bacilli themselves, but does not seem to have given much importance to the observation. Later (1888) two of his assistants, Roux and Yersin, found the same to be true of filtered cultures of the diphtheria bacillus. Later it was found that the tetanus bacillus and the bacillus (B. botulismus) of meat poisoning yielded similar soluble poisons.