Survival of Tritrichomonas foetus Stored at −28 and −95°C After Freezing in the Presence of Glycerol *

SYNOPSIS.Tritrichomonas foetus survived much better on extended storage at ‐95 than at ‐28d̀C following slow freezing in the presence of 1.0 M glycerol. There was no significant difference between these temperatures in survival up to 8 days, but thereafter the protozoa continued to die off slowly at ‐28d̀, whereas their numbers remained essentially constant at ‐95d̀ for 128 to 256 days. The trichomonads' motility was much better after storage at ‐95d̀ than after storage at ‐28d̀, and fresh cultures could be initiated from the former much more readily. Other constituents of the suspending medium besides glycerol affect the survival of the protozoa upon freezing. Survival was much better when the protozoa were frozen in the original Diamond's trypticase‐yeast extract‐maltose‐cysteine‐ascorbic acid‐serum medium in which they had been grown than when they were frozen in physiological salt solution or in fresh Diamond's medium. There was no significant difference between survival in the latter two suspending media. The speed and time of centrifugation needed to remove the trichomonads from the medium in which they had been grown had no effect on their survival upon subsequent freezing. Presumably some product or products of the trichomonads' metabolism have an additional protective action which supplements that of glycerol. When frozen in the original Diamond's medium in which they had been grown plus 1.0 M glycerol, an average of 15% of the trichomonads were alive after 128 days' storage at ‐28d̀ and an average of 38% were alive at ‐95d̀C. When frozen in physiological salt solution plus 1.0 M glycerol, these percentages were 8% and 12% respectively.