LAURENS: MONOCHROMATIC LIGHTS. 



279 



of the middle bands among these being 75.0 mm> 70.0 fx/jL, and 47.5 /jl/jl, 

 respectively. 



Five sets of twelve toads each were tested in each of the six double 

 pairs of lights, and since each toad was given eight trials in each com- 

 bination of lights, the total number of trials for the five sets was 

 960 in each single pair of lights or 5760 trials in all. Three of the five 

 sets of twelve toads were the same as were used in testing the reactions 

 to single monochromatic lights, when both the eye and the skin acted 

 as receptors. Two new lots of twelve toads each were, however 



Fig. 3. Curves representing the percentages of negative responses to the four sets of 



wave-lengths, when received through both the eye and the skin ( ); 



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

 lengths as abscissae and precentages of negative 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; 1' = Yellow. 



selected for the other two sets. These tests were, therefore, carried 

 out on 36 separate toads. 



It will be seen, by referring to Table 7, that the results of the tests 

 of the reactions to balanced pairs of monochromatic lights were, in 

 the main, very similar to those obtained in response to single mono- 

 chromatic lights under the same conditions. The numbers under 

 each pair of lights represent the combined results of two sets of trials, 



