1. A strain of the urban form of tropical typhus has been established in guinea-pigs, and maintained in them for more than one hundred generations. The history and characteristics of the strain are given. The clinical criteria of infection are febrile and scrotal reactions.
2. Methods of demonstration of Rickettsia in material from infected guinea-pigs and rabbits are described. In morphology, distribution and staining characteristics these Rickettsia do not appear to differ from R. prowazeki.
3. The infection of rabbits by intra-ocular inoculation of virus has met with only partial success ; the strains rapidly lose virulence, and do not survive beyond the third generation. The results are closely similar to those reported by Nagayo et al., in corresponding infections of rabbits with the virus of typhus exanthematicus, and to those obtained by the authors in corresponding infections with a strain of Rocky Mountain spotted fever.
4. Infection of white rats has been readily secured, and has been of the "inapparente" form.
5. Two monkeys, inoculated intradermally with infected material, showed a mild general reaction only; no lesion developed at the site of inoculation.
6. The results of the Weil-Felix reactions of sera from rabbits and monkeys convalescent from the infection are summarized. Agglutination is of the OX19 type of Proteus X strains, never of the OXK type.
7. The experimental data obtained indicate that the guinea-pig is the laboratory animal of choice for the study of the urban form of tropical typhus.