GROWTH 213 



construction might be more rapid when more building 

 stones are available. But no great increase can be 

 expected. This is borne out by the facts. All increases 

 observed are small if compared with the changes in 

 growth rate brought about by temperature changes. 



It is an interesting and significant observation that 

 while an increase in concentration does not affect the 

 growth rate, the addition of another substrate may. 

 Bad. typhosum was not affected by peptone beyond 

 0.4%, but the addition of sugar doubled the growth rate. 

 Oxygen influenced growth in a similar way. This proves 

 that the growth mechanism can work faster if more 

 energy is available, and that the failure to produce more 

 rapid growth by more food is due to the impossibility 

 of producing more energy by more substrate. 



The solubility of oxygen is so low that an increase 

 in its concentration by aeration will bring about a greater 

 liberation of energy and accelerated growth, though it 

 is primarily a food for energy. 



(e) TEMPERATURE AND GROWTH RATE 



It has already been pointed out, in discussing the 

 relation between temperature and the rate of fermenta- 

 tion, that the temperature coefficient of all biological 

 activities varies from infinite, at the minimum tempera- 

 ture, to zero at the maximum temperature. The 

 temperature coefficient of biological activities is much 

 less constant than that of common chemical reactions. 



However, we may assume that the influence of temper- 

 ature is primarily the same as in normal chemical 

 processes, and that other processes are superposed at 

 very high or very low temperatures. The temperature 

 coefficient may be considered essentially normal, except 

 for some complications at the two extremes. 



