One of the most important factors for the study of endemic Tsutsugamushi Disease is to isolate surely Rickettsia tsutsugamushi from morbid materials. Judging from the fact that the results of the ordinary isolation by the intraperitoneal blind passage in mice were not necessarily satisfactory, investigations were in the first generation of mice carried on comparing intraperitoneal with intracutaneous inoculation of Rickettsia strain. Material of inoculation is 0.2ml, 10(-2)-10(-8) dilution of hepatolienal emulsion of mice which were infected and diseased by IV-strain of "Umayado". 2 groups of mice, the one inoculated with definite quantity of material intraperitoneally and the other intracutaneously, were observed for 30 days in the 1st generation. From 2nd to 4th generation, intraperitoneal passage was tried with 10(-1), 0.4ml hepatolienal emulsion of conditional mice: in the 1st group of the 1st generation that employed intraperitoneal inoculation, the survived during the observation or the suceumbed to infection and yet Rickettsia in their peritoneal fluid was not proved on the microscope, while then in the 2nd group of the 1st generation that employed intracutaneous inoculation, for all mice, living or dead.
By these blind passage from 1st to 4th generation, Rickett is in the peritoneal fluid was observed on the microscope, and disseminating limit was investigated as follows: in case of 1st group was 10(-4) dilution, and in 2nd group 10(-6) dilution of the emulsion by the inoculation at the 1st generation. In short, it is recognized that Rickettsia of the same density and the same quantity, is more easily and surely preserved, when inoculated in the 1st generation intracutaneously than intraperitoneally. This fact suggests that the adoption of the intracutaneous inoculation should be recommended for the isolation of Rickettsia from diseased person and mouse.