58 The Animal Mind 



as the salivary and other reflexes, there is less chance of 

 misinterpretation than when more complicated choice pro- 

 cesses are involved. 



In all experiments where behavior alone is the basis of 

 inference regarding sensory discrimination, we need to take 

 the utmost care that the animal is really responding to the 

 stimuli, and not to some other accidental cue. Thus a 

 dog in the Harvard laboratory was apparently discrimi- 

 nating accurately between two lighted areas of different 

 size, but events proved that he was actually responding to 

 slight pulls given by the experimenter on the leash that 

 held him. He failed wholly when he was taken off the 

 leash. Nowadays the careful experimenter always re- 

 mains out of sight and hearing of the animal tested, and 

 is not in contact with it in any way. 



§ 13. Evidence from Structure and Behavior Combined 



As a matter of fact, the argument from structure needs 

 confirmatory evidence from behavior. For clearly the 

 mere presence of a sense organ bearing sufficient likeness 

 to our own to admit of conjecturing its function would be 

 of no value as proof unless it were shown that the sense 

 organ actually functioned. In order to do this, it would 

 be necessary to show that the animal reacted to the stimulus 

 conjectured as appropriate to the sense organ, and that 

 removal of the organ profoundly modified the reaction. 

 Thus we shall find that many experiments to test sensory 

 discrimination have been made by the method of extir- 

 pating a sense organ and studying the effect on behavior. 

 The method has many disadvantages, the chief of which 

 lies in the fact that it is hard to say which disturbances 

 in behavior are due actually to the loss of the organ and 



