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,, 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 « stand for the unperformed reactions. Then we have 
N—vw probable reactions to S,.} Habit rendering the 
previously most performed reactions the most probable 
throughout we should expect to find the appropriate re- 
action in response to 
S, contained in N. 
S, contained in N — 4. 
53 contained in N — uw, — 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 
