52 Animal Intelligence 
The advantage due to experience in our experiments is 
not, however, the same as ordinarily in the case of trained 
animals. With them the associations are with the acts or 
voice of man or with sense-impressions to which they natu- 
rally do not attend (e.g. figures on a blackboard, ringing of 
a bell, some act of another animal). Here the advantage 
of experience is mainly due to the fact that by such ex- 
perience the animals gain the habit of attending to the 
master’s face and voice and acts and to sense-impressions 
in general. 
I made no attempt to find the differences in ability to 
acquire associations due to age or sex or fatigue or circum- 
stances of any sort. By simply finding the average slope 
in the different cases to be compared, one can easily demon- 
strate any such differences that exist. So far as this dis- 
covery is profitable, investigation along this line ought now 
to go on without delay, the method being made clear. 
Of differences due to differences in the species, genus, etc., 
of the animals I will speak after reviewing the time-curves 
of dogs and chicks. 
In the present state of animal psychology there is another 
value to these results which was especially aimed at by the in- 
vestigator from the start. They furnish a quantitative esti- 
mate of what the average cat can do, so that if any one has an 
animal which he thinks has shown superior intelligence or 
perhaps reasoning power, he may test his observations and 
opinion by taking the time-curves of the animal in such 
boxes as I have described. : 
If his animal in a number of cases forms the associations 
very much more quickly, or deals with the situation in a 
more intelligent fashion than my cats did, then he may have 
ground for claiming in his individual a variaticn toward 
greater intelligence and, possibly, intelligence of a different 
