178 MIND IN EVOLUTION CHAP. 



the main reasons which lead him to this remarkable 

 conclusion. 



Mr. Thorndike's principal experiments consisted in 

 placing cats, dogs, and chickens in a variety of cages so 

 contrived that they could be opened by means Well within 

 the animal's physical powers, yet quite outside the range 

 of its ordinary experience. Thus clawing at a string, de- 

 pressing a lever, pushing aside a swing door and so forth en- 

 abled the prisoner to escape. It was found that the cat or 

 dog we may confine our attention to them at first clawed 

 and scratched more or less indiscriminately ; in so doing 

 it would in course of time give, by accident, the required 

 push or pull, and so obtain its freedom. After a certain 

 number of repetitions, the animal would acquire the power 

 of doing what was needed more and more quickly, until 

 at last the trick was properly learnt. The right action was 

 " stamped in " by success, while the indiscriminate pawing 

 was stamped out. As a measure of the perfection of the 

 habit, the time required to achieve freedom is taken 

 practically as the sole test. The results are exhibited 

 graphically in " time curves," falling with more or less 

 marked fluctuations from the maximum point of several 

 minutes, to the minimum of a few seconds. Some of the 

 tricks, it may be mentioned, were decidedly complex. One 

 was a " thumb latch " complicated by the fact that after 

 the latch was lifted the door still required a force of 400 

 grammes to open it, and still more by the fact that the 

 latch would "fall back into place again unless the door 

 were pushed out at least a little." Another, called Box J, 

 required two separate movements to open it ; others called 

 K and JL required three such movements. Bearing in mind 

 that the result in these movements would be something 

 utterly foreign to the initial experiences of the cats, and 

 would to the end remain connected only by the observed 

 fact of sequence and not by any perceived continuity, one 

 is somewhat surprised at the measure of success which the 

 animals achieved. All the cats learned some of the tricks, 

 and all the tricks appear to have been learnt by some. 

 The dogs were not so uniformly successful. Let us 

 then examine the grounds on which Mr. Thorndike uses 



