Studies on Experimental Relapsing Fever in Mice

The author studied on experimental relapsing fever using definite numbers of borrelias as the inoculum and the mouse of inbred strains as the experimental animal. For the counting of borrelias in inoculum, Yoshii's new counting slides and the dark field microscopy system were adopted. Borrelia duttonii was utilized as a pathogenic organism of relapsing fever. The results obtained were as follows : 1)　The　LD_50 of the borrelias　for the mouse of A/He strain and its 95 per cent fiducial limits were estimated as 10^6.09±0.61.The degree of borrelemia in the mouse of this strain correlated with the number of borrelias injected and with the severity of resulting borrelemia. The organisms disappeared almost similtaneously in nearly all mice. 2) Of the three inbred mouse strains used, C3H/He was the most susceptible to intraperitoneal injection to the borrelias. This strain also revealed the highest degree of borrelemia and the highest rate of death. 3) The author could not find any connection between susceptibility to the borrelias and the age of the mouse.