TEMPORAL REGULATION IN CELLULAR PROCESSES 



233 



photomultiplier tube b}' means of automatic elevators. There the 

 light emission is detected and then amplified and recorded on a 

 graphic chart ( Fig. 9-2, bottom ) . The vial is brought back up and 

 returned to the turntable, and the next vial is similarly measured. 

 After all samples have been looked at, the cycle is repeated, usually 

 being scheduled to repeat once every hour or once every 2 hours. 



Fig. 9-3. The time of day at which the maximum in the luminescent glow 

 occurred on each of 20 successive days. The values were obtained by measur- 

 ing the luminescence from this vial approximately every two hours, similar to the 

 fashion illustrated in Fig. 9-2, bottom. For the first few days the culture was 

 kept on a daily light-dark cycle, and the peak occurred at the same time each 

 day. Subsequently the light remained on continuously, and whereas the rhythm 

 continued, its maximum occurred about 45 minutes later each day, indicating 

 that the free-running period in this case was 24 hours 45 minutes. Temp. 24° C. 



The chart record in Fig. 9-2 shows six replicate samples on con- 

 stant dim light, assayed once every hour. Peaks of the glow are 

 readily discernible but are evidently somewhat broader compared 

 to those from the sample kept in the dark. 



The values for each vial are tabulated and curves plotted sepa- 

 rately, and then the time at which the peaks occur is recorded. The 

 data may be presented as in Fig. 9-3 where we plot values for the 

 time of maximum luminescence taken from a single vial which we 



