266 PHYSIOLOGY OF BACTERIA 



broth to sugar-free broth. The only source of energy 

 then is some peptone or amino acid. The available 

 amount is less per molecule of substrate. How many 

 molecules per second of the new substrate can be utilized 

 by the cell has not been determined as yet. Doubtless, 

 the enzyme furnishing energy from peptone is a different 

 one from that which ferments sugar. These new enzymes 

 must also be arranged in definite position to the synthetic 

 catalysts in order to make them profit from the energy 

 potential. 



We saw that Bad. typhosum grew twice as fast with sugar + 

 peptone than with peptone alone. It may be that sugar gave a 

 larger amount of energy per molecule. It may be that the energy 

 yield per molecule was not greater, but that more enzyme molecules 

 of this type were present, producing a larger total of energy per unit 

 time. It may be that even the total energy per unit time was not 

 greater, but that the enzyme attacking the sugar is situated in a 

 more favorable position in the cell, closer to the catalysts, while 

 with the more distant protein-attacking enzymes, which produce 

 perhaps more energy, most of the energy is lost by conduction or 

 radiation. 



By selecting the right kind of organisms and of energy sources, 

 and by applying calorimetry as well as chemical analysis, these 

 questions could be decided to a certain extent. The probability 

 of obtaining a better understanding of the growth processes is greater 

 with bacteria than with any other experimental organism. 



(c) VARIABILITY OF THE GROWTH RATE 



Starting from the facts that in most cells, there is 

 only one gene of each kind per cell, and that all genes 

 must have doubled before the cell can divide, the author 

 (1932) developed a theory of the variability of the 

 growth rate. If a large number of uniform cells (i.e., 

 cells with the same kinds and numbers of molecules 

 in the same arrangement) are kept in a uniform, favora- 

 ble environment, there are two possibilities for the order 



