328 PHYSIOLOGY OF BACTERIA 



heat of bacteria. The same range of temperatures is 

 involved in both; the temperature coefficients are very 

 high in both cases, well above 10 for a 10°C. increase. 



The resemblance is also borne out by the circumstance 

 that dry bacteria are much more resistant to heat than 

 moist bacteria. A further similarity is the very great 

 influence of very small amounts of acid upon protein 

 coagulation and upon the death rate of bacteria. The 

 theory of Chick that ''death through heat is due to the 

 action of water upon some one protein which is essential 

 for the life of the bacterium and that the character of 

 this reaction is conditioned by the chemical action of 

 water upon its constituent proteins," seems quite well 

 founded. 



Temperature coefficients of ordinary chemical reactions are 

 considered fairly constant. High temperature coefficients according 

 to Skrabal (p. 321) should increase with decreasing rate of reaction, 

 i.e., with lower temperatures. This explains why we ordinarily 

 speak of definite coagulation temperatures. A drop of a few degrees 

 makes the reaction almost immeasurably slow. 



In the discussion of maximal temperatures, (p. 215), it has been 

 shown that growth and fermentation fail at this point because the 

 rate of regeneration is slower than the rate of deterioration. We 

 were dealing there with cell constituents such as enzymes which 

 can be produced by the cell, and which are present in the cell in a 

 fairly large number of molecules. Temperatures just above the 

 maximum may lead to death by endogenous catabolism if prolonged. 



Death by heat which follows the logarithmic order is probably a 

 different chemical process; it seems to be due to the inactivation of 

 at least one most sensitive gene. It seems reasonable to compare 

 this inactivation with the coagulation of proteins. 



We know nothing about the borderline between death through 

 the destruction of genes and death through the destruction of enzymes 

 or similar catalysts. The observation that the logarithmic order 

 is not always followed when the rate of death is exceedingly slow, 

 may be due to this change from one cause of death to another. 



