In a study of the growth of chicken osteoblasts in cultures exposed to supranormal temperatures of 42°C., 44°C., 47°C., 50°C., and 52°C., it has been observed that:

1. There is no lethal effect after prolonged exposures at 42°C. and 44°C.

2. Cultures are killed after an exposure of 105 minutes at 47°C., of 6 minutes at 50°C., and of 3.5 minutes at 52°C.

3. A definite inhibition of growth occurs after different exposures at all temperatures from 44°C. onwards (see Table I).

4. There is a latent period of approximately 24 hours before any discernible effect of sublethal or just lethal exposures; this latent period appears to be independent of the duration of the sublethal exposure and of the temperature.

5. The high temperature coefficients for lethal exposures and for exposures just sufficient to inhibit growth indicate an underlying "destructive" process in the cells of the culture.

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