36 ROBERT M. YERKES 



sary to burden the reader with further details of conditions or 

 results, except possibly with respect to the general illumination 

 and its relation to the reactions. In some of the series, general 

 illumination was not employed, and it was naturally apparent 

 that the doves could distinguish the stimuli much more easily 

 than when the surroundings were illuminated. It was deemed 

 desirable to use general illumination in order to guard against 

 choice on the basis of the visibility of the sides and floor of the 

 stimulus chambers, for naturally enough, this differed greatly 

 in the light and the dark chambers in the absence of general 

 illumination. On the whole, it seemed very much more satis- 

 factory to conduct experiments in the general illumination pro- 

 duced by a two candle power frosted carbon incandescent lamp, 

 at a distance of 110 cm. above the center of the partition be ween 

 the stimulus chambers. 



As an aid to rapid reaction, the alleys of the experiment-box 

 were kept dark except at the moment of entrance of the dove. 

 In each alley was placed a low-power lamp which could be turned 

 on the instant the door F was raised, and turned off the instant 

 the door H was opened. This served to induce the dove to enter 

 the alley- way and to hasten through it to the food-box. After 

 a few daily series, the birds made the trip quickly and volun- 

 tarily, seldom loitering in the passageways and usually passing 

 from entrance chamber to discrimination chamber rapidly. 



The food placed in the entrance chamber as a motive for 

 return to that portion of the experiment-box was milk-soaked 

 bread, with a small quantity of cracked corn added. During 

 a large portion of the series, the birds ate little, unless they were 

 practically deprived of food while in the living-cage. It is thus 

 fair to say that the process of habit formation in the case of 

 doves 3 and 4 depended almost solely upon punishment, whereas 

 the process in the case of birds 1 and 2 depended solely upon 

 reward. 



As in the writer's previous use of punishment, the induced 

 current was used by means of a Porter inductorium with a 

 number 6 Columbia dry cell as source of current. In the early 

 experiments, no attempt was made to keep the feet of the birds 

 moist, and as a consequence, the secondary coil had to be placed 

 well over the primary. Its position was varied somewhat from 



