The work of Buxton and others showing that normal rabbit serum is capable of killing large numbers of typhoid and paratyphoid bacilli and that the sera of rabbits highly immunized against typhoid and paratyphoid bacilli do not kill these organisms is confirmed; it is emphasized, therefore, that the titer of an immune serum as determined by the usual dilution method with the addition of complement is not an indication of the bactericidal power of the blood plasma in vivo.

The bacteriolytic power of normal and highly immune antityphoid rabbit serum for typhoid bacilli is neither increased nor decreased by the intravenous injection of a large dose of typhoid bacilli; the serum of a rabbit that has received only one or two immunizing injections shows a distinct, but not a great, increase in its bactericidal power at five and twenty-four hour intervals after such an injection.

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