RESPONSES TO MONOCHROMATIC LIGHT 7 



tests upon Polly, a rabbit which Professor Washburn kindly 

 gave us; one used in her recent light work. Polly had been used 

 to working in illumination and nothing would induce her to 

 work steadily in darkness. All of the other animals worked 

 perfectly under the conditions of the experiment. The animal 

 which is trained while young to work in a dark room goes about 

 the task in a perfectly normal manner. 6 



The marks of the animals are given as follows: 



Rat I. Pure white rat, male: fed with blue. 



Rat II. Pure white rat, male : fed with yellow. 



Rat III. Hooded black and white rat, male: fed with blue. 



Rabbit. Gray Belgian Hare, male: fed with blue. 



It will be seen that the records are not inter-comparative. 

 The two white rats were working with different positive colors. 

 Rat III, although fed with the same color as Rat I, was a black 

 and white rat and consequently possessed pigmented eyes. These 

 differences are especially noted in order that too great uniform- 

 ity in records may not be demanded. 



Table II shows the records made by each animal. We began 

 with two stimuli, then on the 22nd day changed to one stimulus. 

 On the 38th day we changed back to two stimuli. Punishment 

 was introduced in each case on the day designated. 



A careful consideration of these records shows, we think, 

 that the discrimination between yellow and blue was not per- 

 fected during the time limits of the experiment. Had we desired 

 to prolong the work the habit would probably have been formed. 

 The paper of Hoge and Stocking (this Journal, vol. II, p. 43) 

 shows that a habit of responding to one of two white lights, 2 

 and 16 cp. respectively, can be formed by the rat in about 500- 

 600 trials. Had the difference in' intensity been less, a much 

 larger number of trials would probably have been necessary. 

 On the assumption that the animals used in the present experi- 

 ment were reacting to a difference in intensity, we would expect 

 the habit to be formed after a sufficient number of trials. Un- 

 fortunately there are no intensity experiments on the Weber- 

 Fechner law in the cases of rats and rabbits to guide us. Since 

 more than 500 trials were given we assume that the relative 



6 Indeed our experience during the past two years at Hopkins has given us com- 

 plete confidence in the dark room work. Any argument advanced concerning the 

 " unnaturalness of the conditions " should be supported by experimental proof 

 before receiving consideration. 



