1. Observations are reported on the virulence of various types of spirochetes and filtrable viruses after storage at – 787deg;C. for periods up to 3 years.

2. Five specimens of Treponema pallidum belonging to 4 different strains, and 7 specimens of T. pertenue belonging to 5 different strains were tested after storage for approximately 3 years. With one exception each specimen contained actively motile treponemes, and all specimens were highly pathogenic for rabbits. Many other specimens of these spirochetes stored for shorter periods were also tested with similar results.

3. Relapsing fever spirochetes tested after storage from 6 months to 1 year showed active motility and were virulent for mice.

4. Leptospira icterohemorrhagiae was found to be actively motile after storage for 5, 6, and 10 months. The spirochete of rat bite fever, Spirillum minus, was virulent for mice after storage for 1 year.

5. The virus of human influenza, PR8 strain, tested after storage for approximately 3 years was fatal to mice in essentially the same dilution as was the same lot of material before freezing. Similar results were obtained upon testing the virus of meningopneumonitis after storage for 3 years. The virus of lymphogranuloma inguinale was pathogenic for mice after storage for 10 months.

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