72 HARRY MILES JOHNSON 



to hesitate when she approached the region where she had 

 tripped before. Twice she jumped when she passed near where 

 the rope had been stretched at the previous triah The experi- 

 ment was not continued further at that time, as prolongation 

 of the tests seemed to be mere cruelty. 



The same test w^as now given to Dog 5, the normal male. 

 He always ran around or jumped over the board. The first 

 trial given after the rope was stretched he tripped over the 

 rope, turning a complete half -somersault. In subsequent trials 

 he always jumped. The rope w^as held in the same place for 

 three successive trials and then removed. In the next three 

 successive trials when the animal reached the place where the 

 rope had been stretched he jumped as he had jumped when the 

 rope was there. The rope was then stretched again, two feet 

 nearer the animal. This time the dog tripped by jumping too 

 late — i.e., he jumped at about the same place as in the pre- 

 vious trials. In subsequent trials he always adjusted himself 

 correctly. 



The same tests were repeated on Dog i a week later. She 

 avoided the board from the first, by means of what sense- 

 avenues we of course do not know\ She never succeeded in 

 adjusting herself to the rope, however, always jumping too 

 late or too soon. 



These crude tests are further indication of the slight use of 

 vision by the normal dog, and made it seem improbable that 

 Dogs I and 2 would change their mode of attack on the prob- 

 lem-boxes because of the little vision they seemed to have. 

 Accordingly it was decided to discontinue this work on them. 

 It seemed questionable, however, whether better results might 

 not be obtained by using animals which had not been kept in 

 the blind state as long as had these. This was the reason for 

 having the same operation performed on Dogs 7 and 8. I wish 

 to say in this connection that our experience has not shown 

 this operation useful for this work. It is not in itself cruel, 

 and the only serious inconvenience which the blind puppies 

 showed was their inability to compete with the normal puppies 

 during the nursing period. The normal puppies would follow 

 the mother into places in the animal's yard where the blind 

 puppies would not go, and would often nurse when the blind 

 puppies were not even present. After weaning, Dog 7 and 



