During the past few years there has occurred a revival of interest in the study of the nature of infection with the pneumococcus. It will be impossible to review all the discoveries of interest and importance that have been made. The intention is to confine the present discussion mainly to certain observations made by my colleagues and associates and myself, which seem to have some value in enabling us to obtain a clearer conception of the process in pneumonia. Certain of the hypotheses advanced must be considered to be purely tentative and further work may show that different explanations are the correct ones.
Biologically as well as clinically the course of lobar pneumonia consists of these phases: First, there occurs the infection and onset of the symptoms, which events may or may not be simultaneous; second, the clinical disease itself or the intoxication; and third, the recovery or immunization, using