The unclassified strains known as Group IV have been separated into twenty-nine types which are designated by the Roman numerals IV and XXXII. Only a small percentage of the pneumococcus strains isolated in New York City for this study were left unclassified.

The majority of the types gave very slight cross-reactions, the exceptions being Types II and V, III and VIII, VII and XVIII and XV and XXX.

In the series of cases studied, Types IV, V, VII and VIII were found more prevalent in the lobar pneumonia of adults and Types V, VI a and XIV in children.

The majority of the types were also found in normal individuals and in persons having respiratory infections other than pneumonia. Types VI a and XIX were most prevalent in the limited number of strains studied by us.

Fourteen of the types were found in pneumococcus meningitis; Type XVIII was found most often.

Antisera suitable for clinical trial have been prepared for fourteen types. From the majority of the horses inoculated for more than a year, antisera having 500 to 1000 units per cc. were obtained. Antisera of lower potency were concentrated and preparations obtained equal to or stronger than high grade unconcentrated serum.

Potent bivalent antisera have been prepared for types which were found to give marked cross-agglutination reactions.

The results with each type as to prevalence, severity of cases, presence in normal individuals, and in spinal meningitis, potency of antisera produced for therapeutic trial and virulence of strains for mice have been considered under the different type headings.

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