130 Animal Intelligence 
former signal and fed the cats, sometimes the latter and did 
not. The 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 thesecond 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 com- 
binations 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 (Fig. 22), one show- 
are ing the decrease in fail- 
a : ures to respond to the 
1 2 wrong signal. The first 
BiG: ae: 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 1 mm. being the 
representative of one failure. Thus, the entire curve 
stands for 280 trials, there being no failures after 60 trials, 
and only 1 after the goth. 
In the other curve, also, each 1 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 an- 
imal learned that the second signal was different from the 
first. The experiment shows beautifully the animal method 
of acquisition. If at any stage the animal could have 
isolated the two ideas of the two sense-impressions, and felt 
