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bulletin: museum of comparative zoology. 



1. All the lights used produced positive responses. 



2. Blue light was the most effective stimulus in the production 

 of these responses, and green, yellow and red lights formed a decreas- 

 ing series, corresponding roughly to their relative positions in the 

 spectrum, the red being but slightly more effective than darkness. 



3. The same sort of reactions were obtained when only the eye, 

 or only the skin, was exposed, as when the whole body was exposed. 



Fig. 2. Curves representing the relative distribution of effectiveness in tlie spectrum, 



wlien tlie Uglits are received tlirough both the eye and the sldn ( ) ; tlirough 



the eye only ( ) ; and through the skin only ( ) . Wave-lengths as 



abscissae, and percentages of positive responses as ordinates. Points marked 

 on axis of abscissae are the positions of the wave-lengths of the middle band of 

 each light. B = Blue; G = Green: R = Red; F = Yellow. 



4. After the eye was excised (Table 4), exposing the eye region 

 to a narrow beam of light produced practically no positive responses. 



5. Illumination of small areas of skin by a narrow beam of light 

 (Table 5) produced positive responses, and the same percentage of 

 responses on each of the three areas stimulated. 



