6 JOHN B. WATSON AND MARY I. WATSON 



approaches the threshold, as on March 9th, a disturbance imme- 

 diately manifests itself. Whenever the green was cut out the 

 animal behaved exactly as though no light stimulus was present 

 (contrast tests on June nth with those on June 12th). These 

 results seem to show that we are dealing here with a defect in 

 the receptor rather than with the lack of "attention" cited in 

 Dr. Weidensall's report. 



Summarizing the results of Experiment I we find: 



1st, that the green was the effective stimulus; 



2nd, that the red had no stimulating effect, — it probably was 

 not discriminated from total darkness. The results harmonize 

 with the hypothesis that the red chosen lay outside of the 

 animal's spectrum. Decisive experiments upon this point now 

 in progress, but carried out under different conditions, will soon 

 be reported upon. 



It is clear that Experiment I does not touch the problem of 

 sensitivity to differences in the wave lengths which lie within 

 the animal's spectrum. 



EXPERIMENT II 



On account of the fact that in Experiment I only one stim- 

 ulus was effective, which made it impossible to test the problem 

 of differential sensitivity with red and green, we began in the 

 fall of 191 1 to test another group of rodents with yelloiu 

 (\=595o) and blue (X=478o). The stimulus lights were not 

 equated in energy during the training series but were projected 

 directly upon the plaster surfaces. To the human eye the yel- 

 low was enormously more intense. Before control experiments 

 began the yellow and blue were equated in energy. The energy 

 value chosen is given by Pfund in the Yerkes and Watson Mono- 

 graph, p. 81. 



January gth. We began taking records upon two gray Bel- 

 gian hares and three rats, — one black and white and two pure 

 white. All of the animals had just reached the age of sexual 

 maturity. We were unfortunate in the case of our rabbits. 

 Not one completed the experiment. All three of the rats con- 

 tinued work throughout the experiment. Experiments upon all 

 five of the animals were begun on January 9th. The training 

 series is given for only four of the animals. The record of only 

 one rabbit is given. We had hoped to carry through all of the 



