ANIMAL INTELLIGENCE. 89 



not naturally as a function of sense-powers discrnmnaic ai all 

 delicately. Thus the cat who climbed up the wire netting when 

 I said, " I must feed those cats !" did not have a delicate associa- 

 tion of just that act with just those words. For after I had 

 dropped the clapping part of the signal and simply used those 

 words it would react just as vigorously to the words, ♦* To-mor- 

 row is Tuesday "or " My name is Thorndike." The rtsu 

 naturally was to a very vague stimulus. Taking cat 10 when just 

 beginning to learn to climb up at the signal, " I must feed those 

 cats !" I started in to improve the delicacy, by opposing to this 

 formula the formula, " I will not feed them," after saying which, 

 I kept my word. That is, I gave sometimes the former signal 

 and fed the cat, sometimes the latter and did not. Tlie object 

 was to see how long the cat would be in learning always to go 

 up when I gave the first, never to do so when I gave the second 

 signal. I said the words in both cases as I naturally would do, 

 so that there was a difference in emphasis and tone as well as 

 in the mere nature of the syllables. The two signals were given 

 in all sorts of combinations so that there was no regularity in 

 the recurrence of either which might aid the animal. The cat 

 at first did not always climb up at the first signal and often did 

 climb up at the wrong one. The change from this condition to 

 one of perfect discrimination is shown in the accompanying 

 curves, one showing the decrease in failures to respond to the 

 right signal, the other showing the decrease in responses to the 

 wrong signal. The first curve is formed by a line joining the 

 tops of perpendiculars erected at intervals of i mm. along the 

 abscissa. The height of a perpendicular represents the number 

 of times the cat failed to respond to the food-signal in 20 trials, 

 a height of i mm. being the representative of one failure. 

 Thus, the entire curve stands for 280 trials, there being no 

 failures after 60 trials, and only i after the 40th. 



In the other curve, also, each i. mm. along the abscissa 

 stands for 20 trials, and the perpendiculars whose tops the 

 curve unites represent the number of times the cat in each 20 

 did climb up at the signal which meant no food. It will be 

 seen that 380 experiences were necessary before the animal 

 learned that the second signal was different from the first. The 



