Lights of Equal Intensity as Stimuli. 6i 



other beam was reduced by being passed through a revolving 

 sector-wheel, thus giving rise to a succession of flashes and dark 

 intervals which fused indistinguishably in the eye, producing the 

 appearance of a continuous flow of light of low intensity. By 

 adjusting the sector aperture and comparing the lights in a pho- 

 tometer, the two lights could be made physiologically equal. On 

 measuring the physical intensities of the two physiologically 

 balanced lights by means of a radiomicrometer, the intermittent 

 light was found to be about 6 per cent, stronger than the continu- 

 ous light. When the two lights were made equal from the stand- 

 point of their physical intensity and were compared in a photo- 

 meter, the continuous light appeared much brighter than the 

 intermittent one. From these results we conclude that inter- 

 mittent white light is a measurably less efficient stimulus than 

 continuous white light of the same intensity, and that in this 

 respect the action of the retina, like that of the photographic plate, 

 affords an exception to the Bunsen-Roscoe law. The reduced 

 efficiency of intermittent light is probably the result of chemical 

 induction dependent upon the frequent interruptions of the light. 

 The sector wheel (episcotister) is therefore an unreliable means for 

 reducing the intensity of light. 



43 (652) 



Preliminary communication on the cytolytic action of ox-blood 

 serum upon sea-urchin eggs, and its inhibition by proteins. 



By T. BRAILSFORD ROBERTSON. 



[ From the Herzstein Research Laboratory and the Rudolph Spreckels 

 Physiological Laboratory of the University of California.] 



1. It has been shown by Loeb 1 that the eggs of sea urchins 

 {Strongylocentrotus purpuratus and Strongylocentrotus franciscanus) 

 may be fertilized by the blood-sera of mammalia, provided the 

 eggs be previously sensitized by a brief immersion in a solution of 

 SrCl2 which is approximately isotonic with sea water. 



2. I find that if ox-serum be rendered sufficiently potent by 

 dilution (cf. below) the formation of a fertilization-membrane by 



■J. Loeb, Arch. f. d. ges. Physiol., 118, 36, 1907; 122, 196, 1908; 124, 37, 1908; 

 "Die chemische Entwicklungserregung des Tierischen Eies," Berlin, 1909, p. 185. 



