THE GONYAULAX CLOCK 581 



into a separate class from those with a Qio of slightly greater than 1 .0. 



If indeed there were several independently oscillating systems in 

 Gonyaulax, one might suppose that the luminescent system was such 

 an oscillator. Our interest in this possibility was discussed earlier 

 (Hastmgs and Sweeney, 1957b) in connection with the finding that 

 the effect of temperature upon period was similar to its effect upon 

 the amplitude of luminescence. This implied that an inhibitor system, 

 presumed to be specific for the luminescent system, was involved, and 

 that its action was directly upon the luminescent system rather than via 

 a master clock. 



More recent experiments appear to exclude the luminescent system 

 as an independently oscillating system. If cells are stimulated to ex- 

 haustion at a time when they are sensitive to resetting by light (refer 

 to Fig. 7 ) , their luminescent response falls to a low value. The effect 

 of stimulation is thus overtly similar to the perturbation by light, both 

 presumably resuking in an exhaustion of a component (s) of the 

 luminescent system. If the luminescent system were itself a clock, then 

 perturbation by stimulation should be an effective way by which phase 

 shifting could be accomplished. When the luminescence of aliquots 

 was assayed at times subsequent to stimulation, it was found that the 

 rhythmicity persisted, but that no phase shift whatsoever occurred. 

 This tells us not only that the luminescent system is not a clock; it also 

 tells us that its precise chemical status has no effect upon the clock. In 

 other words, there is no feedback from the luminescent system to the 

 clock. These experiments may be of significance in directing our ap- 

 proach toward finding the essential components of the clock, since 

 feedback is a critical property to be expected in any biological clock 

 mechanism. 



If we look for a single biological element or class of elements which 

 may function to regulate a variety of physiological processes, our at- 

 tention is drawn to the nucleus since it does have a "master" role in the 

 control of cellular processes. Is there any known aspect of nuclear 

 metabolism which might be involved in the clock mechanism? From a 

 variety of experiments it seems clear that cell division and the mitotic 

 cycle may be excluded as a possibility. In the absence of cell division 

 the clock continues to run. When cell division does occur, the popula- 



