At Fort Sam Houston, Texas, during the winter of 1917-1918, it was noted that the majority of pneumonia cases presented a clinical type not often seen in civil practice. The patients were highly septic; the pneumonia, for the most part, followed measles, and when not fatal, it often terminated in empyema. It was further observed that the usual type of lobar pneumonia was often complicated by relapses, which were attributed to delayed resolution. The frequency of what we shall call, for the present, septic pneumonia, and its occurrence as a complication of measles, led to an investigation as to the causative organism in this type of the disease, as well as in the complicated, so-called lobar pneumonia. It is well known that the hemolytic streptococcus is almost exclusively the causative organism of complications in scarlet fever cases; and since pneumonia is not an uncommon complication of this disease, we were