A series of 222 strains has been analysed serologically and 156 have been found to react with one or other of four sera prepared with haemolytic streptococci of scarlatinal origin.

Among the 156 strains the four chief types were distributed in the following proportions: 10 of Type I, 57 of Type II, 45 of Type III and 44 of Type IV.

The remaining 66 strains of the series have not yet been classified; though they certainly include individualistic strains, there may be other types to be defined by further analysis.

The four chief types are well defined and can generally be identified by direct agglutination. Cross-agglutination may cause confusion when suspensions are unstable, in which case resort must be made to agglutinin absorption. In addition, certain Type I strains may also agglutinate with Type III serum.

Analysis of clinical data in a series of 100 cases shows clearly that a fairly severe form of scarlatina with greater tendency to complications is often caused by infection with Type II scarlatinal streptococcus; Type II has so far been found only in association with scarlet fever.

There were nine instances where two or more members of the same family developed scarlatina; in six instances the same type was found in each patient and in three each patient yielded an unclassified strain. In one instance the strains from two members of the same family were different.

Haemolytic streptococcus colonies on fresh blood agar present three chief varieties; there are minor differences between these dependent on the amount of moisture in the medium.

There is a certain correlation between variety of colony and serological type. Type III colonies retain a soft consistency after two days' incubation, while the other types generally become tough and can be lifted from the medium as a whole.

Rough and smooth colonies with differential characters analogous to those occurring in pneumococcus cultures have not been identified. An interesting change in appearance is the production of a clear dome-shaped watery or slightly mucinous colony (3rd variety) in a culture which ordinarily forms either more or less opaque or soft coherent colonies.

There is evidence that the proportions of the four main types are likely to vary in different localities and in different outbreaks of scarlet fever in the same locality.

The importance of a reliable classification of haemolytic streptococci is discussed.