LAURENS: MONOCHROMATIC LIGHTS. 297 



Red light, as has ah-eady been pointed out, was less effective in 

 pairs with other lights when received through only the skin, than when 

 received through only the eyes. When paired with blue light, there 

 was 1 % more of movements toward red than there was when the 

 lights were received through only the ej^es. From a comparison with 

 the results obtained with single lights, we might have expected the 

 responses to blue light when received through only the eyes, to be 

 higher than when received through only the skin. 



As was found to be the case in the reactions to single lights, the 

 effects of the stimulation of the two kinds of receptors showed their 

 influence upon the reactions when the whole animal was exposed to 

 the light. The more effective light, in most of the pairs of lights, 

 showed a higher percentage of responses when received through both 

 the eyes and the skin, than when received through only one of the two. 

 The pairs of red with green and yellow, however, do not conform to 

 this, owing to the greater effectiveness of the red light when received 

 through only the eyes, as compared with that when it was received 

 through only the skin. The blue and green had also the same effect 

 on both the eyes and the skin, as on the eyes alone. This was due to 

 the lack of sensitiveness in the skin to dift'erences in wa^'e-lengths at 

 the blue end, when the light was received through only the skin. The 

 green and red showed the same percentage of positive responses to 

 the green when received through both the eyes and the skin, as when 

 received through the skin alone. This was due to the ineffective- 

 ness of red light to stimulate the skin, as well as to the less sensitive- 

 ness of the skin to differences in wave-lengths. The blue light, in 

 pairs with other lights, had very little more stimulating value for the 

 skin than had the green, in pairs, when only the eyes were exposed; 

 still, the blue was plainly more potent than the green. When hoth 

 the skin and the eyes were exposed to the lights, the blue was no more 

 potent than was the green, when the lights were received through only 

 the eyes. This was again due to the fact that the sensitiveness of 

 the skin to differences in wave-lengths in the more refrangible lights 

 of the spectrum was very slight, and that what differences were found 

 in the reactions, when both the skin and the eyes were exposed, were 

 due, for the most part, to the sensitiveness of the eyes. 



There is seen in these reactions to balanced pairs of lights a counter 

 effect of the different sets of wave-lengths. Each of the lights in a 

 given pair seemed to be able to exert its influence on the reactions. 

 The more potent, short-waved light, in any pair, reduced considerably 

 the effect of the less potent, long-waved light, as measured by their 



