TEMPORAL REGULATION IN CELLULAR PROCESSES 



239 



through all the manipulations of adding, centrifuging, rcsuspending, 

 etc., without adding any inhibitors (Fig. 9-7). Note that in these 

 controls there occur appreciable variations. TJiere are some few 

 cases where the phases differed b\- 2 hours. The fact that these 

 occur normally must not be overlooked. But in general it is evident 

 that the reproducibility in the controls is good; the variance is small. 



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TIME 



Fig. 9-7. A series of control experiments to illustrate the accuracy of the 

 experimental procedure. (See text and legend to Fig. 9-5 for details.) 



From this we have concluded that chemical or inhibitor pertur- 

 bations may lead to less accuracy, i.e., to an increase in the observed 

 variance, but that the precise effect, i.e., whether we see a phase 

 advance or a phase delay, may differ from one experiment to the 

 next. We would, therefore, emphasize that the assay system should 

 be tested for variance with manv controls as illustrated here and 

 that any suspected phase shift ascribed to particular conditions 

 should be repeated manv times to assure that one is not simply 

 looking at increased inaccuracy. 



