SUMMARY: An examination of freshly isolated strains for agglutinability, growth requirements, haemagglutination, virulence for mice, alum precipitability and protective properties shows that each of these characters varies quantitatively, and furthermore that they vary independently. The presence of one strongly marked character is no indication that another character will be strongly marked or even present. Not all strains necessarily have the character to be expected in freshly isolated strains; one or possibly more may be missing. On subculture of the strains on Bordet-Gengou media the order in which these characters degenerate or are lost and the rate at which they are lost differs with the strain. Agglutinability and agglutinogen content vary considerably in freshly isolated strains, and therefore the expression ‘agglutinates to titre’ cannot be considered as a criterion of a Phase I organism. The obvious complexity of the serology of organism within ‘Phase I’ suggests that this term has served its useful purpose and should now be dropped as a description of a certain type of strain. The term ‘Smooth’, which indicates the possession of the antigenic components commonly associated with the pathogenic state of the organism, is preferable.


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