GROWTH 227 



Above the optimum, we can assume the deterioration of 

 some essential part of the growth mechanism with a high 

 temperature coefficient. Such assumption would lead 

 to the Tammann principle which has actually been 

 observed in a number of cases. Growth rates are con- 

 stant below the optimum temperature, and decreasing 

 with time above the optimum, decreasing the more 

 rapidly the farther the temperature is above the opti- 

 mum. The decrease will ultimately lead to death. 



The minimum temperature is not as yet explained 

 in a generally accepted way. One possible explanation 

 is the assumption that the slowness of energy liberation 

 does not allow the cells to accumulate enough energy to 

 accomplish some essential synthesis, or repairs. 



(/) CHEMICAL STIMULATION OF THE GROWTH RATE 



In the study of chemical stimulation of fermentation, 

 an analogy was drawn between the action of poisons and 

 the action of temperature. With isolated enzymes, 

 an immediate acceleration of enzyme activity was found, 

 followed by a greater decrease due to a more rapid 

 enzyme destruction. In fermentation by living cells 

 which can regenerate the enzyme, a continuous accelera- 

 tion of the fermentation by stimulants was assumed 

 to be possible. 



In the case of chemical stimulation of growth, the 

 analogy with temperature may well be continued. Let 

 us assume, for the sake of simplicity, that the rate of 

 fermentation remains uninfluenced by the concentration 

 of the stimulant which affects growth. Two processes 

 are stimulated by the poison acting as a catalyst: the 

 cell sjmthesis, and also the deterioration of the growth- 

 producing agent. This agent is deteriorating normally 

 in all cells, though quite slowly, and is constantly being 



