SUMMARY: Vaccines were prepared by formolizing cultures of and precipitating with aluminium hydroxide gel (AG). Fifty per cent of mice were protected against about a thousand lethal doses. Two (Ru and VYS) of eleven strains yielded highly potent vaccines.

Serum in the medium increased the potency of vaccines and for one of the strains liver extract was needed in the medium to give potent vaccines. In general, vaccines protected well against heterologous strains but protection was relatively poor against one of these.

A soluble antigen present in culture fluids induced in rabbits antibodies protecting mice and agglutinating suspensions of grown in the presence of serum. This soluble antigen was thermo-labile. In these respects it resembles the L-antigen, differing only in being detached from the surface of cells. Soluble antigen was precipitated with AG, yielding fairly good vaccines. Cells freed from media were also precipitated, yielding rather better vaccines. It is suggested that cells yield vaccines of high potency when they have produced and retained a relatively large amount of L-antigen.


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