1. A simple method for freezing and maintaining tissue specimens in a mixture of solid carbon dioxide and 95 per cent ethyl alcohol at a temperature approximating –78°C. is described.
2. When frozen and maintained at this temperature Treponema pallidum and Treponema pertenue, upon thawing, exhibited normal morphology and motility and their virulence for rabbits was not appreciably altered after periods of at least 1 year. This applied to a number of different strains of each organism. The infectivity of material in which treponemes were scant was maintained as well as of material in which they were abundant.
3. At temperatures of –10°C. and –20°C. syphilis treponemes did not survive as long as 2 months. Death of the organism occurred not at the time of freezing but during the maintenance period.
4. Treponemes did not commonly survive freezing and desiccation, although one lot of dried material which contained T. pallidum was infective for rabbits 1 day after desiccation.
5. The viruses of human influenza, yellow fever, and spontaneous encephalomyelitis of mice when frozen and maintained at –78°C. showed substantially the same titer after 6 months as before freezing.
6. Certain practical applications of the method are suggested.