A biological classification has been made of thirty strains of Friedländer's bacillus. This study reveals that there exist among these strains three sharply defined and specific types and one heterogeneous group. The three types are Type A, fifteen strains; Type B, six strains; Type C, three strains; and Group X, six strains. The agglutination, agglutinin adsorption, protection, thread, and precipitin reactions have been employed in the working out of this classification, and the types have been proved highly specific by means of each serological test.

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1. Pneumococcus extracts have been shown to be capable of producing hemorrhagic purpura in white mice, rabbits, and guinea pigs. 2. The purpura-producing principle resists heating to 100°C. for 10 minutes; it resists oxidation; it is filter-passing; its activity is destroyed by digestion with trypsin; it is obtained from pneumococcus extracts by full saturation with (NH4)2SO4, after the acetic acid-precipitable substances have been removed from the extracts. 3. The purpura-producing principle is common to all four types of pneumococcus and apparently bears no relation to virulence. 4. The purpura-producing principle is probably a degradation product of pneumococcus. 5. This principle is not associated with the hemotoxin of pneumococcus, since the hemolytic activity of an extract may be destroyed without effect on the ability to cause purpura.

1. Under proper conditions mass R cultures of Friedländer's bacillus may give rise to a number of variants which are dissimilar in colony appearance and morphology. Three such forms have been described. In two varieties, differences have been observed not only in colony formation and morphology, but also in cultural and antigenic characters. 2. None of the methods employed were adequate to cause reversion of any of the R variants to the S type. Growth of the R2 variant in its own antiserum, however, induced a change to the R1 form. 3. R forms of Friedländer's bacillus may be derived from S strains by aging or by growth in anti-S serum of the homologous type. 4. R strains may be isolated in culture directly from infection. In the cases where R forms were found, S cells were also present, and the pathological condition was of a chronic nature.

In a preceding paper (1) evidence was presented that bacilli of the Friedl~nder group are separable into sharply defined and specific types. Of 30 strains employed in the study, three specific types and a heterogeneous group were demonstrated by agglutination, agglutinin adsorption, protection, thread and precipitin reactions. These types have been designated Type A, Type B, and Type C, while the remaining unclassified strains were placed in a tentative group, Group X. In the light of the present studies, the difficulties encountered in previous attempts to interpret the immunological reactions of Friedl~nder's bacillus appear to be due hi large measure to the failure to distinguish in the cell the type-specific from the speciesspecific antigen; and the failure to recognize in immune serum the two distinct antibodies provoked by the respective antigens. The application of this concept to the Friedl~tnder group was suggested by studies carried out in this laboratory on the immunological relationships of the cell constituents of Pneumococcus (2-7). Briefly, this concept involves two separable and distinct antigens--the one a soluble specific substance (now identified as a carbohydrate) which endows the organism with type specificity; the other, a protein substance which exhibits only the common and undifferentiated characters of the species.Since the relation of the capsular material of Friedl~nder's bacillus to type specificity has been demonstrated (1,8,9), it seemed of importance to determine the immunological relationships of encapsulated and capsule-free strains of this organism. For this purpose, S and R varieties of the bacterial cell were obtained as will be de-683 on