GROWTH 



247 



The rate of energy supply is constant as long as there is 

 a fair amount of substrate (e.g., sugar) available. With 

 a low amount of energy food, and sufficient building 

 material, there will be a definite growth. If the energy 

 food is increased, growth will not be more rapid, but will 

 continue longer, because there is an energy supply for a 

 longer time, which will ultimately produce a larger crop. 

 Assuming sufficient building material, further increases 

 of energy food will bring about further increases of the 

 crop as is illustrated schematically in Fig. 24. In actual 

 practice, the accumulating fermentation products or cell 

 secretions will retard the growth rate after a while, and 

 will make the utilization of the food less effective. 



One of the most commonly quoted experiments is that of Rubner's 

 (1906a) with BacL vulgar e grown in different concentrations of 



