The characters of the Aronson Streptococcus from Prof. Neufeld's laboratory at the “Robert Koch” Institute in Berlin have been described. This coccus resembles the pneumococcus in many respects, viz. the appearance of the colonies on the surface of horse blood agar, its virulence and capsule production in mice and rabbits, the production of a specific precipitable substance in the peritoneal washings of infected mice, the formation of firm clumps and masses when mixed with homologous antiserum, the ease of production of active and passive immunity in mice and rabbits by intraperitoneal and intravenous inoculation, the alteration in the morphology of colonies, i.e. the appearance of R forms, associated with attenuation of virulence. It differs from the pneumococcus in the following features: the round shape of the cocci, bile-insolubility and the absence of autolysis in surface colonies, the beta haemolysis of deep colonies in horse blood agar, the production of a soluble haemolysin in broth cultures, the difficulty of producing active immunity in mice by the subcutaneous injection of heat-killed vaccines.

I have obtained the Aronson Streptococcus (Neufeld type), which Lance-field places in a group containing chiefly streptococci of bovine origin, from human throats, but there was no evidence in any instance that it was producing disease, and it seems probable that it is not pathogenic for man.

The results of my investigation of this strain are in agreement with those of Yoshioka (1923), Killian (1924) and Lancefield (1933, 1934).

There are in existence other laboratory strains designated Aronson Streptococcus. These have been found to exhibit specific characters identifying them with the Str. pyogenes. It is proposed that the name Streptococcus Aronson should be confined to strains possessing the characters of Aronson N above described.