ioo The Dancing Mouse 



Situations which are potentially beneficial to the animal 

 attract it in varying degrees according to its internal condi- 

 tion; situations which are potentially disagreeable or in- 

 jurious repel it with a constancy which is remarkable. The 

 favorable stimulus solicits a positive response; the unfavor- 

 able stimulus demands a negative response. 



Finally, in connection with the discussion of motives, it is 

 an important fact that forms of reward are far harder to 

 find than forms of punishment. Many animals feed only at 

 long intervals, are inactive, do not try to escape from con- 

 finement, cannot be induced to seek a particular spot, in a 

 word, do not react positively to any of the situations or con- 

 ditions which are employed usually in behavior experiments. 

 It is, however, almost always possible to find some disagree- 

 able stimulus which such an animal will attempt to avoid. 



As it happens, the dancer is an animal which does not 

 stand the lack of food well enough to make hunger a possi- 

 ble motive. I was driven to make use of the avoiding re- 

 action, and it has proved so satisfactory that I am now 

 using it widely in connection with experiments on other 

 animals. The use of the induction shock, upon which I 

 depended almost wholly in the discrimination experiments 

 with the dancer, requires care ; but I am confident that no 

 reasonable objection to the conduct of the experiments could 

 be made on the ground of cruelty, for the strength of the 

 current was carefully regulated and the shocks were given 

 only for an instant at intervals. The best proof of the hu- 

 maneness of the method is the fact that the animals continued 

 in perfect health during months of experimentation. 



The brightness discrimination tests demanded, in addition 

 to motives foV<pkyiee, adequate precautions against discrimi- 

 nate oQri <> >y r tfther t&ali- visual factors, and, for that matter, by 

 other "visual* fetcto,feo'trian that of brightness. The mouse 



