LAURENS: MONOCHROMATIC LIGHTS, 



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TABLE 2. 

 Reactions of toads to monochromatic light received through the eye only. 



The numbers under + indicate total numbers of reactions toward the light; 

 under — , away from the light; under ±, without reference to the Hght (indifferent); 

 imder 0, no reaction within five minutes. 



corresponded to the sequence in the spectrum with bhie as the most 

 effective stimulus, and red as the least. There were only 55 % of 

 positive responses in red light, 44 % of negative, and 1 % of no reaction, 

 within five minutes. A decrease of 5% would therefore make the 

 percentage of positive responses equal, under this stimulus, to the 

 sum of the percentages of negative responses and no reactions. While, 

 therefore, the red light, owing to the presence of the 55 %. of positive 

 responses, must be regarded as more effective than darkness in the 

 production of responses, it cannot be regarded as much more so. 



By way of summarizing the results of the experiments with only 

 the eye as receptor, it may be said that they were essentially the same 

 as when both the eye and skin acted as receptors. Blue light was the 

 most effective stimulus in the production of positive responses, and 

 the other lights formed a decreasing series, following the sequence in 

 the spectrum, red light being only slightly more effective than darkness. 



C. Reaciions urith the Skin a^ Receptor. 



Having demonstrated that the eye was concerned in the reactions 

 in which the whole body was exposed to the light, it remained to test 

 the skin in this respect. To do this, it was necessary that the eye be 

 protected from illumination. Hoods, made from the finger-tips of 

 fairly heavy rubber gloves, were placed over the snouts of the toads 



