REWARD AND PUNISHMENT IN HABIT FORMATION 247 



CONCLUSIONS 



1. On the whole subjects showed no marked preference between 

 the light and the dark box but the experimenter found four rats, 

 all belonging to the same litter, which were decidedly positive 

 phototropic. Two of these animals always chose the light box 

 and the other two took the light box eight out of ten trials. But 

 this must not be taken to have any bearing on the question of 

 light or dark preference in rats under ordinary light conditions, 

 for the light used in this experiment was not only very weak, 

 being 0.61 candle power, but was softened by the ground glass 

 bulb. 



2. When the experimenter attempted to use a period of hunger 

 of forty-eight hours he found that rats fifty-six days old could not 

 undergo so long a period of starvation but were by the third or 

 fourth series physically unfit for use. 



3. The above facts led us to establish two preference series 

 of ten trials each and to use subjects older than fifty-six days, 



EXPERIMENT PROPER 



Subjects used in the experiment proper were seventy-eight days 

 old on the day that the training series began. Each animal was 

 given one-half hour daily in the control box for five days preced- 

 ing the training series in order that the subject might become 

 familiar with the box and the place where food might be found. 

 In addition to this each subject was given two preference series 

 of ten trials each on the two days preceding the training series. 



Special conditions of the experiments. The experiments were 

 done in four sets, each set consisting of a group of animals trained 

 with electric shock and a group trained with hunger. For the 

 first set the strength of electric shock was one hundred and fifty 

 units and the length of the period of hunger was forty-eight hours. 

 For the second set the strength of electric shock was one hundred 

 and fifteen units and the period of hunger was thirty-one hours. 

 For the third set the strength of electric shock was seventy-five 

 units and period of hunger twenty-four hours. For the fourth 

 set the strength of electric shock was sixty units and the period of 



