GROWTH 189 



reasons. This part is usually quite small with the type 

 of organic changes usually met in fermentations. 



During the period of rapid growth, more energy is utilized 

 in cell construction than in the later stages of development. 



SUMMARY OF THEORIES 



It is generally believed that growth is impossible 

 without a source of energy. The amount of energy 

 required for growth seems quite considerable. In 

 peptone media and in milk, the total energy content 

 of the construction material is similar to that of the cells, 

 i.e., their combustion heats are similar, but a special 

 source of energy seems still necessary. Even when the 

 energy content of the building stones is much higher 

 than that of the cells (methane, amines) growth takes place 

 only when accompanied by oxidation or fermentation. 



Perhaps, the formation of certain essential cell com- 

 pounds requires a definite potential which can be main- 

 tained only by a special and continuous source of energy. 



Since fermentation continues after growth has ceased, 

 young cultures must show a better efficiency in the 

 utilization of energy than the older ones. There is no 

 indication that during the lag phase, or at the very 

 earliest period of rapid growth, energy is utilized better 

 than during the immediately following period of rapid 

 growth. 



in. THE GROWTH RATE 

 (a) METHODS OF MEASURING THE GROWTH RATE 



The growth rate, or more correctly, the rate of multi- 

 plication, is ordinarily measured by a computation 



