226 PHYSIOLOGY OF BACTERIA 



To account for such adaptations biochemically seems almost 

 impossible with our present knowledge of the cell mechanism. 



SUMMARY OF FACTS 



Temperature influences the growth rate greatly. 



At very low temperatures, the time required for a 

 cell to double may be more than forty-eight hours. 

 The same organism could double at the optimum tem- 

 perature in half an hour. 



There is a definite low temperature at which a culture 

 will cease to grow. Near this point, the time required 

 for a cell to double increases rapidly with a decrease of 

 temperature and finally becomes infinite. At tempera- 

 tures below this minimum, the cells die slowly. 



From a point about 10°C. above the minimum to the 

 optimum temperature, the rate of growth will be increased 

 from two to three times by a 10°C. rise in temperature. 



Above the optimum temperature, the growth rate is 

 not constant, but decreases with the time. During a 

 first short interval, it may be higher than the rate at the 

 optimum temperature, but it does not last. 



A culture grown for a while at low temperatures will 

 grow more rapidly at low temperatures than a culture 

 of the same strain precultivated at high temperatures. 

 Bacteria and yeasts can be adapted within limits to 

 low and high temperatures. 



SUMMARY OF THEORIES 



Growth must be considered as the sum of a number 

 of slow chemical reactions, all of which are accelerated 

 by an increase in temperature. Growth must have a 

 fairly normal temperature coefficient. 



The maximum and minimum temperatures of growth 

 are brought about by the superposition of other processes. 



