S. SPIEGELMAN AND A. M. CAMPBELL 



synthesis in individual cells relatively more rapid than the time of 

 the experiment, and if a lag period in the onset of enzyme forma- 

 tion were normally distributed in the cell population, one would 

 obtain a cumulative curve of enzyme with time which would 

 have the appearance of a logistic. Benzer (8) was able to dem- 

 onstrate that this was not true under conditions of gratuity by 

 the ingenious use of bacteriophage as a tool. The virus was 

 employed here both to stop enzyme formation and to release the 

 enzyme by lysis of those cells which had accumulated enough 

 enzyme during the period of induction to support virus multi- 

 plication. Using this device he demonstrated that enzyme 

 synthesis is uniform in all cells in gratuitous inductions but is 

 heterogeneous if the inducer is the primary or sole energy 

 source. 



This question has not been completely resolved in yeast. 

 An interesting attempt to do so was, however, made by Terui 

 and Okada (97), who photomicrographically examined the 

 distribution of the division times in a population of cells in which 

 the energy required for the division was derived from the in- 

 ducing substrate maltose. They come to the conclusions that 

 the kinetics of the over-all adaptation is explainable on the basis 

 of a normal distribution of lag times in the population. There 

 are certain features of the experiment which make for uncer- 

 tainty. By its very nature, it is performed under nongratuitous 

 conditions which, according to Benzer's results, lead to inhomo- 

 geneities. Further, onset of division may not be an adequate 

 measure of induction level. Finally, as has already been noted, 

 it is relatively easy to change the kinetics of enzyme formation in 

 the very system these authors studied from the logistic to one 

 which is linear with time. Whereas one can explain logistic 

 kinetics on the basis of a normal distribution of lag times, it is 

 virtually impossible to explain linear kinetics on a similar basis, 

 since it would involve assuming a completely unrealistic dis- 

 tribution. 



Monod, Pappenheimer, and Cohen-Bazire (56) examined 

 the kinetics of beta-galactosidase formation in E. coli by the use 



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