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1. Silver nitrate or sodium merthiolate can be used for the sterilization of suspensions of B. typhosus and neither have any immediate destructive effect on the Vi, O or H antigens.
2. Two methods of employing silver nitrate as a sterilizing agent are described.
3. Physiological saline solution with silver nitrate added is bactericidal for B. typhosus and the staphylococcus but has no inhibitory action on the growth of moulds.
4. Vaccines sterilized and preserved with silver nitrate after storage for 6 months at 7° C. were found to have retained their Vi antibody stimulating properties.
5. A vaccine sterilized and preserved with “katadyn” after storage for 18 months at 7° C. still contained some Vi antigen and was superior as an immunogenic agent to a freshly prepared heat-killed-phenolized vaccine.
6. It would appear that the stability of Vi antigen is increased by the addition of silver within certain limits, but this effect is only obtained if low temperature storage conditions are maintained.
7. A vaccine sterilized and preserved with sodium merthiolate after 6 months' storage at 7°C. failed to stimulate any Vi antibody in the rabbit.
