190 CHARLES A. COBURN 



When the crow chose the correct path, it was always rewarded 

 with a bit of food, — a small piece of mouse, frog, or other meat. 

 If it chose incorrectly, it received no food and was required to 

 remain three or four minutes in the exit-box, which had been 

 previously darkened by a cloth thrown over the wire side. The 

 dislike of crows to remain in a darkened chamber was utilized 

 also by the gradual darkening of the entrance-box when the 

 crows hesitated too long before entering the discrimination- 

 chamber at the beginning of a test. This never failed to cause 

 them to leave immediately. There were, therefore, at least two 

 motives for correct choice, namely, the desire for food and the 

 dislike of the darkened box. The latter can be considered a 

 constant factor, for they reacted to the darkened box as strongly 

 at the end of the summer as they did at the beginning. 



Care was taken throughout the experiments to keep the fac- 

 tor of hunger constant. It was impossible to do this at all times, 

 and it is highly probable that the results in many cases were 

 materially affected by the change in this factor. 



In the beginning, two series of five tests each were given per 

 day. The times for the beginning of these series varied slightly, 

 but as a rule they were 7 :30 A. M. and 1 :00 P. M. The crows, 

 with this number of tests, would still be hungry at the end of 

 the series, so the number of tests per series was raised to ten 

 and the amount of food given at the end of each correct choice 

 was lessened. It soon became apparent that the crow, in this 

 case, was confined too long. After the seventh or eighth test, 

 it usually busied itself more with getting out of the apparatus 

 than with choosing the correct path in order to get food. On 

 this account, three series, (7:30 A. M., 12:00 M. and 4:00 P. M.), 

 of eight tests each were given per day. Finally the number of 

 trials in each series was changed to five, and this seemed to be 

 the best solution of the problem, as the crows were sufficiently 

 hungry three times a day to be eager to get food. In the major- 

 ity of cases, they were still hungry at the end of a series. The 

 time required for the five tests was rarely over ten minutes, 

 and the crows, as a rule, did not become restless in this time. 



As a rule, one crow was given all the trials of a series before 

 the other was caught. In a few series, the crows were given 

 alternate tests. This was not conducive to the best results, for 

 the crow, waiting in the entrance-box until the other completed 



