48 FREDERICK S. BREED 



to show that, as a rule, a chick with a full crop is not so good 

 material for an experiment like this as one not so well fed, but 

 these animals while being experimented upon did not always 

 rush about for food as soon as they had reached the cage. 



IV. Experiments 



In these experiments on modification thirty-eight chicks were 

 used. The work was done from Dec. 15, 1907 to June 30, 1908. 

 To test the interrelation of habits of response to optical stimuli, 

 the necessity arose of discovering at least two methods of measur- 

 ing modifiability in this sense mode. It was desirable in the 

 case of any one method that the stimuli bear such a relation 

 to each other that the average chick could complete the training 

 within a reasonable time, and that the time should be as nearly 

 as possible constant for different chicks. The feasibility of the 

 electric shock and satisfactory conditions and devices for train- 

 ing the chicks were determined upon after several hundred 

 preliminary trials in a crude reaction box. The apparatus 

 shown in figures 8 and 9 was constructed on the basis of experi- 

 ence in these preliminary tests, combined with the suggestions 

 afforded by the apparatus of Yerkes ' and that of Hamilton ^ 

 used in similar experiments. Means for retaining the animal in 

 the entrance box until it made movements to escape, permitting 

 it meanwhile to be within range of the stimuli; the location 

 of these stimuli at a suitable distance from the point of release; 

 the open screen overlooking the cage — these features were 

 planned with characteristic activities of the chicks in mind. 

 Releasing the chick too soon or too late at any given trial pro- 

 duced unsatisfactory results. If the cards were too near, the 

 pulse of activity often carried the animal into the electric box 

 before the card stimuli had wrought the proper effect. And when 

 the animal had made an error and had arrived at the closed exit, 

 the chicks in the cage below acted as an additional stimulus to 

 escape. The animals readily found the exit through H when the 

 door was open. 



A. Color 



In all the color work the reflection method with the Bradley 

 standard colored papers was employed. Hue, tint, and shade 



'Yerkes, R. M.: The dancing mouse. New York, 1907, p. 92. 

 ' Hamilton, G. V. : A study of trial and error reactions in mammals. The Journal 

 of Animal Behavior, 1911, vol. I, p. 33. 



