LAURENS: MONOCHROMATIC LIGHTS. 



289 



of different wave-lengths, while much reduced at the most effective 

 end of the spectrum, still must be regarded, in all essential respects, 

 as similar to that of the eyes, though much reduced throughout. 



B. Lights of the same Wave-lengths. 

 Reactions with both the Skin and the Eyes as Receptors. 



There could hardly be any doubt that the lights from the two 

 generators were the same, not only in the range of wave-lengths 

 shown to occur in them by spectroscopic examination, but also in 

 their relative intensities, as shown by radiomicrometric readings. 

 It seemed desirable, however, to test further these conditions experi- 

 mentally, and the following trials were accordingly made. 



The generators were so adjusted as to deliver lights of the same 

 wave-lengths and intensities, and the toads were tested in the field 

 between these two presumably equal sources. The results of these 

 tests are given in Table 10. Two sets of twelve toads each were tested. 



TABLE 10. 



Reactions of toads to balanced lights of the same wave-lengths received through 

 both skin and eyes. 



The numbers under A indicate total numbers of reactions toward the light 

 from generator A; under B, toward the light from generator B; under I, without 

 reference to either light (indifferent) ; under 0, no reaction within five minutes. 



each set being given 96 trials in each pair of lights, and therefore a 

 total of 192 trials for the two sets of toads. The procedure, orienta- 

 tion, etc., were precisely the same as carried out in the tests of the 



