240 JOHN D. DODSON 



in like experiments we did not care to require an animal to retain 

 the habit for so long a time as six or nine days. 



Care of subjects. Subjects which were trained with electric 

 shock were fed twice daily just as were the animals which were 

 not being used. The subjects which were trained with hunger 

 were fed in the same way except during the period of training. 

 The group trained with twenty-four hours of hunger was fed 

 the last time, before the experiment, at three.-thirty in the after- 

 noon of the day prior to the day of the experiment. Thirty 

 minutes after feeding the rats were transferred to a cage in which 

 no food was ever put and kept there until the time of the experi- 

 ment. The group trained with thirty-one hours of hunger was 

 fed at eight-thirty a.m. and transferred at nine a.m. of the 

 day prior to the day of the experiment. The group trained 

 with forty-one hours of hunger was fed last at ten and transferred 

 at ten-thirty p.m. two days before the day of the experiment. 

 The fourth group, trained with forty-eight hours hunger was fed 

 at three-thirty and transferred at four p.m. two days before the 

 day of the experiment. 



Training with- electric "shock. Af"the beginning of each experi- 

 ment all doors of the control box were closed except the one at 

 the exit of the light box . Th^e food receptacle had been removed on 

 the day before and all food cleaned off the box and the openings 

 closed. The subject was placed in the nest box and allowed 

 to pass into the choice box where it faced the dual possibility of 

 entering the light or dark electric box. If it chose the light box 

 it could pass out at the exit and through the alley to the nest box 

 without receiving any shock; but if it chose the dark box it re- 

 ceived an electric shock and it had to return through the entrance 

 chamber and the light box in order to get to the nest box. The 

 shock was given to the animal after it had entered the electric 

 box instead of as it entered as is the usual method. This was 

 to make the place of punishment as nearly comparable to the place 

 of food as was possible. 



Training with food. At the beginning of the series of experi- 

 ments with food, food was placed in the receptacles and all doors 

 closed as in case of the training with electric shock. If the sub- 



