60 SECRETS OF ANIMAL LIFE 
to the floor of the aquarium. One arm was made 
rough internally, and at its upper end the snail 
received an electric shock, of which the roughness 
was meant to be the “warning.” The smooth arm 
of the tube led to the surface of the water, where 
fresh air is obtained—sufficient reward in itself. 
The experiment consisted in pressing the air from 
the snail’s lung and then placing it at the base of 
the so-called labyrinth. It is of value to the snail 
to get its lung filled as soon as possible; this is 
attained by creeping up the smooth arm, it is missed 
by creeping up the rough one; and the failure is 
emphasized by a mild punishment, the slight electric 
shock. But the result of the pretty experiment was 
to show a complete incapacity to profit by experi- 
ence to the extent of solving the problem. The 
percentage of error did not diminish as the series 
of trials lengthened; indeed, things sometimes got 
worse instead of better. 
In one interesting set of experiments a power of 
forming associations was displayed, but it was 
not, so to speak, followed up. Both arms were 
smooth, but the wrong road had as its warning 
notice-board an irritating hair which was made to 
touch the snail’s horns and the back of its head. 
Immediately on the heels of the warning, if the 
snail persisted on its wrong course, came the punish- 
ment of a shock. Now, in 15.6 per cent. out of a 
total of nine hundred and thirty trials, the snails 
changed their course from the wrong to the right 
path after contact with the warning stimulus, but 
