GROWTH 215 



Without making any further assumptions about this 

 growth-producing agent, we must assume that it is 

 destroyed rapidly at high temperatures, and therefore 

 it must be destroyed slowly at low temperatures. We 

 have seen the same behavior in enzymes. 



Just as we have assumed a continuous slow deteriora- 

 tion of the endo-enzymes in living cells (p. 131), so we 

 may assume a gradual slow deterioration of the growth- 

 producing agent in the cell. iVnd just as under normal 

 environment, the cell is continuously rebuilding the 

 endo-enzymes as fast as they deteriorate, keeping the 

 enzyme concentration of the cell constant, so we may 

 assume that the growth-producing agent is rebuilt by 

 some part of the cell as rapidly as it deteriorates, and that 

 a cell, in favorable environment, maintains a constant 

 level of the growth-producing agent. 



An increase in temperature will bring about a more 

 rapid action of the agent, i.e., accelerated growth. At 

 the same time, it will bring about a speedier deterioration 

 of the agent, and also a more rapid regeneration of the 

 agent. But these three processes are not accelerated at 

 the same rate. The temperature coefficient for growth 

 is about 2 to 3; the coefficient for the regeneration will 

 probably be about the same. But the coefficient of the 

 deterioration of the agent is doubtless much greater. 

 It must be quite high to account for the short interval 

 between optimal and maximal temperature. We must 

 expect here again a complete analogy with the fermenta- 

 tion processes. 



Since deterioration is accelerated with greater speed 

 than regeneration, there must be a temperature where 

 the regeneration is just barely able to make up for 

 deterioration. This is the highest temperature at which 

 the cell can work with its normal amount of growth- 



