58 STELLA BURNHAM VINCENT 



ment made a break in the series but it lasted only for a day 

 or two. When a rat is hungry he dashes off immediately, prob- 

 ably chiefly under the guidance of his olfactory sense. Here 

 we had hungry rats, but we had produced a situation which 

 not only called for sense discrimination but also for an initial 

 inhibition of this instinctive impulse to run for food. In this 

 particular set of animals the case was made harder because in 

 the 150 previous trials fixed habits of reaction had been formed. 



Although the shock was slight, one experience was enough 

 to establish an association and to check the impulse in its com- 

 plete working out. There was a great difference among the 

 animals in this respect. Some had to reach the plate before 

 it was effective, others stopped at the entrance; some could 

 not carry the association over from one day to another, some 

 from one trial to another; and some rats lay at the entrance 

 quivering all over, not from fear as they often ventured on a 

 live plate without showing anything like this behavioj-, but 

 apparently wHth excitement as though the restraint put upon 

 the impulse to i-un had caught all other impulses in a leash 

 and produced an emotional condition which at first w^as inhib- 

 itory of all action. 



"F," a rat in group (b), which had made one of the best 

 records previously, when put in the box always ran straightway 

 down some pathway as chance directed, but he never made but 

 one error per trial for after this punishment he always stopped 

 to "nose" at the next entrance. He was the last of his group 

 to learn the box, but in the last 100 trials he never made but 

 one error per trial. He had to have the shock before the first 

 impulse to run could be blocked. On the contrary "A," group 

 (a), whose records had been good previously immediately made 

 the required per cent of correct choices. 



When this halt came, most animals developed activities which 

 tended to multiply the sense stimuli, particularly the cutaneous 

 and the olfactory. Heads were put in pathways before ventur- 

 ing in, the sides of the partitions were brushed by noses and 

 vibrissae in running down a path, the whole body was often 

 pressed hard against the side. As a result, animals began more 

 and more to turn away from or turn back in the wrong path- 

 ways, after such activities and seek other roads to success. It 



