Investigations made since the above was written show that this micrococcus does vary greatly in its pathogenic power when obtained from different sources, and that virulent cultures obtained from the blood of inoculated animals become attenuated when they are kept for a short time. This, indeed, is a general rule as regards the best-known pathogenic bacteria; which usually acquire increased virulence when cultivated in the bodies of susceptible animals, and become attenuated as regards their pathogenic potency when they are cultivated for a certain length of time in artificial media. My own experiments with pneumonic sputum were made in January, 1885, and led me to the identification of the oval coccus, commonly in pairs, which is found in this material, with the coccus which I had previously found in my own saliva (September, 1880), and which was subsequently the object of extended experimental researches made by me in 1881-1884.
In my paper read before the Pathological Society of Philadelphia, in April, 1885, I say: "It seems extremely probable that this micrococcus is concerned in the etiology of croupous pneumonia. . . . But this can not be considered as definitely established by the experiments which have thus far been made upon the lower animals." The extended researches of Frankel, Weichselbaum, Netter, Gamaleïa, G. and F. Klemperer, and others, which have been published since, have fully established the etiological rolé of the micrococcus in question.
In 1882 Fehleisen isolated the so-called streptococcus of erysipelas and proved by experiment that it is the etiological agent in the production of erysipelatous inflammations. At a later date (1884) Rosenbach isolated the micro-organisms commonly concerned in traumatic infections and in the production of acute abscesses. Among these was a streptococcus, called by him Strep-
