1. Cultures of typhus fever rickettsiae were as a rule found to remain viable and virulent after being stored at 37° and –20°C. for several months, whereas they failed to survive when stored at the intermediate temperatures of 20° and –4°C. for 4 weeks and 10 days respectively. In one instance cultures were stored at 37°C. for 8 months without having been transferred, and were subsequently found to be viable and infectious.

2. The conditions influencing such long survival of an organism which seems to require living tissue for multiplication (as filterable viruses do in general) are discussed.

3. Typhus-infected tissues (minced guinea pig tunica) suspended in a serum-Tyrode mixture in sealed flasks remained infectious at 37°C. for at least 10 weeks.

4. Additional evidence for the etiological significance of the rickettsiae in typhus fever is obtained from the experiments described.

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