1. The serological investigations of the O, K and H antigens of the coli group have led to the establishment of a diagnostic antigenic schema by means of which the coli strains can be classified in O groups and types.

  2. Besides the O and H antigens, the K antigens (either envelope or capsular antigens) play a very important rôle. The K antigens include thermolabile antigens (L and B antigens) as well as thermostable antigens (A antigens). While the L and B antigens mostly are envelope antigens (corresponding to the Vi antigen), the A antigens appear mostly as visible capsules (corresponding to the pneumococcus capsule). Thus the term “K antigens” is a symbol for a group of different antigens, including envelope antigens and capsular antigens.

  3. A few O groups are particularly frequent, and this applies also to certain types within these groups. A very high percentage of the strains belonging to these O groups and types are O-inagglutinable—on account of the K antigens. The O group distribution differs in normal and pathologic materials. Therefore, also the type distribution must differ, but the present material is not sufficiently large to establish the percental distribution.

  4. Strains containing K antigens are more toxic than strains without K antigens—and particularly toxic when the strains are isolated from pathologic material.

  5. The toxicity is a constant and characteristic type quality, differing in the individual types of an O group.

  6. Hemolytic and necrotizing strains are particularly frequent in O groups 2, 4 and 6. O inagglutinability of these groups is due to L antigens, that of groups 8 and 9 usually to A antigens.

  7. There is a connection between the type of a strain, its origin, O inagglutinability, hemolytic power, necrotizing capacity and toxicity.

  8. Strains with K antigens are particularly resistant to the defensive forces of the organism and to bacteriophages.

  9. It is suggested as a working hypothesis, that there are certain serological coli types which possess a particular pathogenicity and play an important rôle in appendicitis, peritonitis, cystitis, pyelitis and other diseases.

  10. In the coli group, cultural tests play but a minor rôle, so that the type division has to rest on a serological basis. The prevailing classification of the coli strains, based on cultural criteria (especially fermentation tests) should therefore be abandoned.

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