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475quantitatively estimated by determinations of the rate of cellular respiration. The results were checked by morphological examination of the frozen incubated tissue and by in vivo growth. 2. Measurements of the rate of respiration were reliable as an index of survival if the cells were incubated for more than 2 hours at 37°C following freezing, and if they were suspended in a physiological medium compatible with normal survival and recovery of injured cells. 3. Krebs-Ringer-Phosphate medium was unsuitable, but equal parts of partially neutralized horse serum and Krebs-Ringer-Phosphate provided an adequate medium. 4. The respiration and survival of sarcoma-37 cells, pretreated for 2% to 3 minutes in the ethylene glycol in Krebs-Ringer solution then frozen in liquid air was 50 to 60% of the unfrozen controls. 5 . The respiration of untreated frozen sarcoma-37 was not usually significant. Morphological analyszs of these tissues indicated fewer than 1% surviving cells in most experiments. 6. Y o significant difference in survival was observed between the rapidly and slowly frozen tissues. 7. Good correlation was observed between the morphological and respiratory characteristics of the frozen incubated tumor cells. L _ _ _ _ _ _ 1. Luyet, B. J., and Gehenio, P. M., Life and Deat h at L o x I'e~trperat~~re, Biodynamica, 1940. 2. Luyet, B. J., Freezing and Drying, Hafner Pub.