GROWTH 265 



original problem, the chemistry and dynamics of the 

 growth process. 



Some information might be obtained from the obser- 

 vation that growth is hardly accelerated by increases of 

 concentration of either substrate or building materials 

 while it is greatly influenced by a change of the substrate, 

 or by a change of temperature. 



Bad. typhosum in peptone solution had a generation 

 time of about forty minutes, with 0.4% peptone as well as 

 with 1% peptone (p. 204). But with the addition of 

 glucose, the growth rate doubled. Bad. coli in 1% 

 peptone solution showed a generation time of thirty-five 

 minutes and quadrupling this amount gave only 13% 

 increase in the growth rate; the same effect which this 

 additional 3% of peptone produced, could be obtained 

 by as little as 0.1% of sugar (Curran, 1925). 



Quite different is the effect of temperature upon 

 growth. It influences fermentation, increases the energy 

 yield per unit time. Concentration of food cannot do 

 that. 



A certain food will give a definite amount of energy. 

 The enzymes in the cell can ferment only a limited 

 number of substrate molecules. For Strept. ladis at 

 20°C., this number was estimated to be about 1,000,000 

 molecules per second. Increasing the sugar concentra- 

 tion will not cause more molecules to be decomposed. 

 The enzymes are working with maximum capacity. 

 But an increase in temperature brings about the decom- 

 position of more molecules by the same number of 

 enzymes; the mechanism is accelerated; everything 

 moves more rapidly. 



A change of substrate changes the rate of energy 

 formation. We have no means of telling exactly what 

 happens when a streptococcus cell is changed from glucose 



