Since the publication of the work of Lancefield1on a serologic differentiation of human and other groups of hemolytic streptococci it has become increasingly evident that by the precipitin reaction these streptococci probably fall into a number of "groups" which are of fundamental systematic significance and of great practical importance. The groups so far recognized are indicated by the letters A, B, C, D, E, F, G, H and K. Evidence so far accumulated by various investigators indicates that most of the human pathogens, and certainly those responsible for epidemics of septic sore throat and scarlet fever, belong to group A. Although sporadic cases of human infection by streptococci of some of the other groups have been reported, there is reason to suspect that for man these streptococci are opportunist pathogens of little or no epidemiologic significance. On the other hand, it has been found that hemolytic streptococci of