Serological study of a large number of strains of indifferent streptococci has revealed the existence of a large homogeneous group to which the designation Type I has been applied. It is recognized that members of Type I are not necessarily identical, and that further division into subtypes may be feasible. All strains of Type I ferment inulin and salicin.
The remaining strains are referred to as belonging to Group X. They are distinguished only by their failure to react strongly with Type I serum. While at present this group must be regarded as quite heterogeneous, further work may reveal the presence of other as yet undefined types now included within its limits. The organisms of this group vary in their fermentative reactions with both inulin and salicin.