254 Journal of Comparative Neurology and Psychology. 



Intensity of the electric stimulus is, then, important in connec- 

 tion with rapidity of hahit-formation. Since, however, no differ- 

 ence in sensitiveness appears to be correlated with age differences 

 we may assume, until we know otherwise, that the age differences 

 in rapidity of learning are not due to the influence of the electric 

 stimulus. But, at the same time, since the males appear to be 

 raore sensitive than the females, it may be that the sex differences 

 in rapidity of learning are in part at least due to the influence 

 of the stimulus. Possibly the particular combination of condition 

 of discrimination and strength of stimulus was more favorable 

 for the one-month males than for the comparable group of females, 

 and possibly also for the females, as a whole, the combination of 

 conditions was more favorable than for the males. 



The significance of this suggestion will be clearer in the light of 

 the results of the next section of this paper, for in that we shall 

 have to examine data, which, if I could have foreseen them at the 

 beginning of my work with the dancer, would have altered almost 

 all of my experiments. I do not wish to give the reader the impres- 

 sion that I regard the results of the plasticity experiments as value- 

 less or that I consider this investigation of mine exceptional in 

 comparison with the work of any or all other investigators in this 

 field. On the contrary, I have great respect for both the experi- 

 mental procedure and the results which it yielded, but I am espe- 

 cially interested in pointing out the complexity of conditions which 

 the investigation has revealed. 



Before turning to the topic of the next section, I wish to call 

 attention to the probable significance of the law of habit-formation 

 which I have tentatively formulated above. As I have stated it, 

 this law may not hold for other conditions of habit-formation, or for 

 other animals. Only further investigation along lines which Mr. 

 Dodson and I have followed can decide these questions. Mean- 

 while, it is evident that the subject is of great importance, for 

 much of our experimental work in animal psychology rests upon 

 the assumption that the stronger the stimulus which conditions a 

 particular act the sooner the animal will learn to perform that 

 act. In the light of our results concerning the relation of strength 



