Hamilton, Unusual Reaction of a Dog. ^^^ 



of particular interest beyond a progressive decrease of errors, and 

 an increase of correct first choices. The experiments were dis- 

 continued after sufficient data had been obtained for purposes of 

 comparison with those to be obtained from the more comphcated 

 experiments about to be described. 



Experiments with colors, colors and odors, and odors alone. — 

 At the i6ist experiment the white sign board and white pedal card 

 were discarded. The green sign board was hung in position, the 

 green pedal card was placed in p i (the first pedal to the left), the 

 black pedal card in p 2, the yellow pedal card in p 3, and the red 

 pedal card in p 4. There were sixteen diff^erent combinations of 

 this sort, so arranged that each color was represented upon each 

 "pedal attached" once in sixteen times, and upon each "pedal 

 unattached" three times in every sixteen. Each of the four pedals 

 was attached four times in a series of sixteen experiments. An 

 irregular order of attaching pedals and placing pedal cards was 

 followed in order to prevent the animal from learning a sequence; 

 but care w^as taken that no one pedal should be attached twice in 

 succession, that no one color should occur as the sign of "pedal 

 attached" twice in succession, and that every pedal card should 

 be shifted to a different pedal after each experiment. 



At the 481st experiment the colors were reinforced by odors: 

 red by lupulin, black by asafoetida, green by castor oil, and yellow 

 by beef extract. Thus, if the yellow pedal card (now reinforced 

 by the beef extract odor card, suspended from its anterior sur- 

 face) were on the attached pedal, the yellow sign board was hung 

 out with a beef extract odor card attached to it. At the 581st 

 experiment the colors were abandoned, and only odor cards and 

 odor sign boards were used. These were attached to plain sign 

 boards and pedal cards, identical in form with those that bore the 

 colors. 



It can be seen from the above that an adequate reaction to the 

 situation required the animal first to seek the sign board, then to 

 inspect it, and finally, to strike the pedal bearing the only card 

 that would afford him the same odor or visual stimuli that he got 

 from the sign board. In this connection it may be said that it was 

 impossible to determine positively whether or not he was ever 

 guided by the colors as such, or even by their differences in light 

 intensity, although the latter increased rapidly in the order from 

 black to yellow. It is probable that the colored papers had each 



