HOMOLOGOUS AND HETEROLOGOUS PROTECTION IN MICE VACCINATED WITH THE TWO TYPES OF MOUSE TYPHOID BACILLUS.

A saline vaccine prepared from our stock strain of M. T. II produces in mice definite protection against the homologous strain, and perhaps some slight cross-protection against M. T. I also. Two vaccines prepared with our stock strain of M. T. I failed to produce any definite protection in mice even against the homologous strain, nor was any cross-protection afforded against M. T. II.