270 Animal Intelligence 



appropriate reaction. When the appropriate reaction is 

 finally given, the other reactions are not called into play, 

 S may cease to act, but until the appropriate reaction is 

 given let the organism be such that it runs through the 

 gamut of the others until the appropriate reaction is brought 

 about. As there are N possible reactions, the chances are 

 that the appropriate reaction will be given before all N 

 are performed. At the next appearance of the stimulus, 

 which we may call S 2 , those reactions which were in the 

 last case performed, are, through habit, more likely to be 

 again brought about than those which were not performed. 

 Let u stand for the unperformed reactions. Then we have 

 N u probable reactions to S 2 . Habit rendering the 

 previously most performed reactions the most probable 

 throughout we should expect to find the appropriate re- 

 action in response to 



Sx contained in N. 



5 2 contained in N u v 



5 3 contained in N u^ 



S contained in N nu, which approaches 

 one as a limit. 



Thus the appropriate reaction would be fixed through the 

 laws of chance and habit. This law of habit is that when 

 any action is performed a number of times under certain 

 conditions, it becomes under those conditions more and 

 more easily performed " (Journal of Comparative Neurology 

 and Psychology, 1908, Vol. XVIII, pp. 503-504). 



This hypothesis is, like Professor Jennings', adequate to 

 account for only the one special case, and is adequate to 

 account for that only upon a further limitation of the number 

 of times that the animal may repeat any one of his varied 

 responses to the situation before he has gone through them 



