194 C. F. CURTIS RILEY 



white light is used. It is evident that red light is not a very 

 effective form of stimulus, certainly the toads are not nearly 

 so responsive to it as they are to white light. 



In the experiments with blue light the toads are observed to 

 be distributed at various different points in the experimentation 

 dish. This is placed in the beam of light emerging from the 

 blue solution. The animals turn with promptness toward the 

 source of illumination. In most cases they jump immediately 

 toward the light, or with a delay of but a few seconds. There 

 are comparatively few pauses between the jumps and these are 

 of short duration. Not only is the orienting response more 

 prompt, but the movement toward the light is also more vigor- 

 ous than is the case when the red solution is used. The orien- 

 tation of the toads and their movement toward the source of 

 illumination are very similar to the results observed with the 

 1 6 c.p. incandescent light when neither the red nor the blue 

 solution is used. 



Torelle (I.e., p. 478) found when single colored lights were 

 used that specimens of Rana virescens virescens and Rana clamata 

 always jumped in the direction of the blue light and remained 

 with their heads pointed toward it, touching the glass. On a 

 frog being placed close to the red light, it usually turned away 

 from the source of illumination. In some cases the animal not 

 only turned, but jumped away from the red light. When a 

 frog was placed about 30 cm. away from the red light, the 

 animal generally remained there and did not jump toward the 

 light. According to the experiments of Pearse (I.e., p. 189) 

 with Rana palustris, 



"The results show that the blue is apparently the most effective in 

 the production of positively phototropic reactions, and that there is a 

 regular graduation from blue to red, both in the percentage of positive 

 reactions and in the rapidity with which the movements took place. * 

 * * It is probable that these differences in the reactions are due to 

 differences of the wave lengths, but they may be due to intensity 

 differences." 



These results of Pearse with R. palustris are largely in accord 

 with those of the writer with young toads. Results similar to 

 those of the writer on young toads when blue and red lights 

 were used were obtained by Laurens (191 1, p. 267). He sub- 

 jected Bufo americanus and Bufo fowleri to the stimuli from 

 single monochromatic lights of equal intensity, using Nernst 



