No. 495] NOTES AND LITERATURE 



215 



The interesting paper of Hamilton 8 is perhaps in its origin 

 independent of the Harvard laboratory. We have seen that the 

 dancing mouse learns to act on the basis of a comparison be- 

 tween two things, selecting, not a particular thing, but the 

 lighter of two, or the darker of two, etc. Kinnaman found 

 that the monkey could similarly learn to choose always the 

 lighter vessel, or to choose the colored vessel from among a num- 

 ber of vessels, even when the colors were changed. Hamilton 

 made a precise study of a similar sort of action in a dog. The 

 animal learned that in order to escape from a pen and get 

 food he must press, out of a number of levers, the one that 

 bore the same sign that was found on a general sign-board 

 elsewhere in the pen. In successful cases his method of pro- 

 cedure was, then, to inspect the general signboard, then to pass 

 in review the four levers till he found the one that bore the 

 same sign — then to press this. This appears to involve a fairly 

 complex mental operation (if we may venture to interpret the 

 actions of animals from that highly reprehensible standpoint). 

 The dog clearly learned to choose in the way described. But 

 unfortunately, being a clever dog, he after a time discovered 

 a much simpler method of action that accomplished the same 

 results. He merely began at one end of the series and pressed 

 the levers in order till he came to the one that worked. When 

 electric shocks were attached to the "wrong" levers, he de- 

 cided that he didn't care to play at that game any longer, and 

 the experiments had to end. 



How far such action, seeming to involve complex mental 

 operations, may be demonstrated in animals when there has 

 been fifty years' development of method and results in such 

 investigations, instead of merely two or three attempts at it, 

 is a question that deserves consideration by those who are so 

 ready to deny, on the basis of what we now know (or rather, 

 on the basis of what we don't know), all mental complexity 

 in animals. 



Indeed, it is clear that much of the work we have just reviewed 

 consists in showing experimentally that the mental operations 

 of animals are more complex than had been supposed; in re- 

 storing to aniin.-ils certain things that had been denied them. 

 And this is typical. The recent history of the study of animal 



•Hamilton, G. van T. An Experimental Study of an Unusual Type 

 of Reaction in a Dog. Journ. Comp. Neurol, and Psychol., 17, 1907, pp. 

 329-341. 



