24 L. W. SACKETT 



checks have been employed showing the amount of the un- 

 conscious influence which the experimenter may have had on 

 the animal's responses. 



The conclusion is that the animal's basis for reaction was 

 something other than the unconscious idiosyncracies of the 

 experimenter. It is thus different from Herr von Osten's horse, 

 and the experimenter has successfully eliminated himself. How 

 the porcupine makes this discrimination between foods cannot 

 be said with absolute certainty. At first it was possible for 

 them to use taste. Smell was always possible though neither 

 of them would furnish reliable criteria to the animal. The 

 fact that the discrimination was made and the hand brought 

 into service while the mouth was yet full of the last morsel 

 and the senses of taste and smell were flooded with its effect, 

 leads the writer to believe that these senses could not have been 

 reliable guides. Vision was, no doubt, the sense depended upon. 

 But whether they used form, size, brightness or color is not 

 certain and not easy to determine. 



In the control experiments now to be described, animals 7 

 to 10 were used, sweet potato being substituted for cabbage. 

 The same conditions exclude taste and smell from the possible 

 sense stimuli. Form and size were eliminated by cutting the 

 sweet potato and carrot into pieces of the same general sizes 

 and shapes. Anticipating some later results it may be said also 

 that color can safely be dropped from the consideration, leav- 

 ing brightness as the most probable and possibly the only cri- 

 terion for discrimination. It seems clear that the seven porcu- 

 pines which have acquired this ability give good evidence of 

 voluntary discrimination followed by a definite muscular re- 

 sponse. The word "voluntary" is used to characterize the 

 reactions particularly significant on the numerous occasions 

 when the food was changed and the animal would start to 

 reach with the hand previously used, in an automatic, or reflex 

 manner. On discovering the changes he inhibited the responses 

 half executed, and reacted at once with the other hand. The 

 experimenter is again sure that there was no involuntary start 

 on his part to cause the animal to inhibit one reaction and 

 change to another. The measure of choice may not be as defi- 

 nite as in Powlow's (51) salivary reflex method with the dogs, 

 but it has the advantage of using voluntary muscles instead of 



