1. The history of a typical sanguineus-borne human case of typhus is given, together with the results of intraperitoneal inoculation of material from the initial lesion into guinea-pigs.
2. This material in the earlier inoculations caused a high mortality rate among guinea-pigs, and is characterized from the other material obtained from rats and fleas by the swing of temperatures between morning and evening.
3. Three cases of non-lesion typhus occurred in a brewery heavily infested with rats and fleas, the patients affirming they had been bitten only by fleas.
A high rat infestation was noted and a Xenopsylla index of 15·0 per rat.
4. Inoculation into guinea-pigs of emulsified brain and testicle material from Rattus rattus trapped at this typhus focus, and of emulsified fleas from the rats, resulted in the establishment of a strain of virus which produced a typhus-like syndrome in guinea-pigs.
5. Infection of guinea-pigs with strains of virus from rats, ticks and fleas, has been secured without any difficulty in Kenya, and it has not been found necessary to keep guinea-pigs on vitamin-deficient diets.
6. Typical scrotal reaction has been observed in the majority of guinea-pigs inoculated. The onset is generally sudden and coincides with the rise in temperature. Subsidence of the swelling and inflammation is gradual over about 3 days.
7. Loss in weight is not a marked feature of the forms of virus encountered in Kenya.
8. Post-mortem appearances in the rat-and flea-forms differ from those of the tick-type mainly in less ascites and slight enlargement of the spleen.