APPENDIX 399 



time. It may be observed directly (p. 267, Table 74), 

 or may be computed from microscopic or plate counts 

 of the numbers of cells in a liquid at the beginning and 

 the end of an experiment, or by the weight of the cells, 

 e.g. in yeasts. The initial number of cells be a, and the 

 number at the end of the experiment, after the time t, 

 be b. Then, we find 



b = a2'*, where n is the number of generations in the 

 time t. Since a and b are known, we find n from the 

 equation 



n = log^- 



or transformed into decimal logarithms, 

 _ log & - log g 



The experiment lasted for the time t; in this time, the 

 cells divided n times; therefore, the time for one genera- 

 tion must be 



t 



^ = n 



Hog 2 



log 6 — log o 



This is the standard formula for the generation time 

 which was given in a somewhat different form as early 

 as 1876 by Pedersen. 



The generation time is not constant during the growth 

 of a culture; it is, a priori, impossible that it can remain 

 constant, because growth cannot continue in a culture 

 for an indefinite time. The multiplication within a 

 limited space soon comes to point where it is retarded 

 more and more, until it ceases altogether, and the 

 generation time becomes infinite. 



