An investigation of the possibility of treating cases of pneumonia with specific antisera other than T y p e I and T y p e I I antisera was undertaken because clinical results indicated t h a t pneumonia cases were benefited slightly, if at all, b y t r e a t m e n t with heterologous antisera. For this purpose it was necessary to classify further the infecting types of pneumoeocci, to prepare diagnostic antisera for their identification and specific therapeutic antisera for treatment.

The pneumococci hitherto known as Group IV have been separated into ten types which have been designated by Roman numerals from IV to XIII. These have been correlated as far as possible with the types described by others. The prevalence and mortality of cases due to each type have been estimated in the limited number of cases studied. Laboratory tests indicated that therapeutic antiserums for Types I, II and III have very little protective power against the recently separated types. Monovalent antiserums of high agglutinative and protective power were prepared in rabbits for each type. Several monovalent antiserums each specific for a type, which are suitable for agglutination and experimental therapeutic use, have been obtained by immunizing horses. An antiserum prepared for one type had very little cross-protective power against other types.

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