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Ellen C. Weaver and Norman I. Bishop 



members' the signal from each of a large number of repetitions of 

 each light and dark sequence. Noise, being random, is averaged 

 out, while any consistent signal, however small, is huilt up to 

 recognizable proportions. 



We devoted most of our attention to the shift at 520 m^a; the 

 ^+78 m|j. shift seems to be related in a direct way to it in that it 

 behaves in a similar way with varying conditions. Fig. Ua is a 

 trace of the rise and decay of this shift in wild type cells; 

 both curves are approximately exponential with the 0.1 second 

 flash employed here. The whole cycle, light plus dark, is two 

 seconds in duration. Fig. 4b at once tells us why we were seeing 

 no shifts with the 3 msec flash in Mutant 11; although the posi- 

 tive shift is rapid, the decay is very much slowed down. If the 

 absorption change is not reversible, the repetitive flash device 

 will detect no change. For Number 8, (Fig. kc) both rise and de- 

 cay of the absorp)tion shift at 525 W- are slow. However, both 



LIGHT 

 ON 



Fig, k Time course of the absorption change at 525 W- produced by 



a neon flash in wild type and mutant Scenedesmus . Each 

 curve is the summation of 100 repetitions of the light-dark 

 cycle, made with the aid of a CAT (see text). 



