1. Horgan's (1936) findings with regard to heat sterilization of B. typhosus vaccine are not confirmed.

2. Silver in the form of katadyne or electro-katadyne appears to be an effective sterilizing agent for B. typhosus suspensions.

3. Katadyne and electro-katadyne have no destructive action on Vi, O or H agglutinogens of B. typhosus.

4. Electro-katadyne, even when used in excessive doses, has no detrimental effect on the immunizing activities of Vi antigen.

5. Electro-katadyne sterilized suspensions of V strains of B. typhosus are more effective immunogenic agents than those sterilized by heat and phenol.

6. The bactericidal properties of electro-katadyne, though impaired in 0·85 per cent saline, are adequate as a means for preserving vaccine.

7. It is suggested that katadyne sterilized suspensions of V strains might be of value in testing for the presence of Vi agglutinins in human sera since they are hypersensitive to Vi antibody while retaining most of their resistance to O antibody.

8. In view of the suggestion by Felix that additional antigens with activities similar to those of Vi antigen may exist in bacteria other than B. typhosus, it may be found that the electro-katadyne process has an application in the preparation of vaccines generally, particularly those which have hitherto proved ineffectual in prophylaxis.