A strain of typhus Rickettsia was recovered from the blood of a patient, an apparently isolated endemic case, and another from body lice collected in his garments. Both strains conformed in all their attributes in guinea pigs, albino rats and mice to the murine type, except for the fact that in guinea pigs the typical Neill-Mooser reaction was absent. Evidence was adduced from our previous observations and from the literature that, contrary to general belief, murine strains do not always produce pronounced scrotal swelling in guinea pigs; some murine strains, as far as their orchitic property in these animals is concerned, may appear to be intermediary between the murine and the human Rickettsiae or resemble the latter. The present strains, though only slightly orchitic or non-orchitic, were therefore identified with the murine Rickettsia. It was concluded that, in North China, as in Mexico, when louse-infested persons contract murine typhus, the body louse may become a carrier of the murine Rickettsia, and, in all probability, may give rise to small or large epidemics under favorable circumstances.