The dynamic nature of thermophily.

1. Evidence for a close relation between thermophilic and mesophilic bacteria is discussed. 2. It is shown that in the absence of nutrients thermophilic bacteria at 55 degrees C. die as rapidly as mesophilic bacteria, and that enzyme systems of the thermophils are rapidly inactivated at this temperature. 3. It is concluded that the thermophils can live at high temperatures because they can synthesize enzymes and other cellular constituents faster than these are destroyed by heat. 4. In order to account for this great synthetic capacity at high temperatures, and for the high minimum temperatures observed for many thermophils, it is postulated that these organisms have a higher temperature coefficient of enzyme synthesis than mesophils.