LAURENS: MONOCHROMATIC LIGHTS. 297 
Red light, as has already 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 eyes. 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 differences in wave-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 both 
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 
