Precise interpretation of our experiments seems to impose the following conclusions:

Guinea pigs inoculated with washed Rickettsiae from Mexican typhus fever develop a disease identical with that resulting from inoculations with whole tunica scrapings, blood or other virulent material, and become thereby immunized to European typhus fever.

The etiological agent of Mexican typhus fever is the Rickettsia body of the type described by Mooser (5) in the tunica vaginalis of infected guinea pigs; and it is likely that the etiological agent of European typhus fever is an organism similar to this, but not identical with it in some of its minor biological characteristics.

This content is only available as a PDF.