THE EDUCABILITY OF A SNAIL 57 
snail’s mouth was touched with a little piece of 
food, such as lettuce, there followed a number— 
about four was common—of rapid mouth-move- 
ments, opening and closing, in fact. These obviously 
correspond, in the logic of the experiment, to the 
mouth-watering of Pavlov’s dog. 
The next step was to find a practicable secondary 
stimulus, and that used was pressure on the snail’s 
foot or creeping sole with a clean glass rod. This 
does not normally evoke any mouth-movement, 
except in rare cases, which are readily explained. 
The next step was to apply simultaneously the two 
stimulations, the touch of food near the mouth 
and the pressure of the glass rod on the foot. To 
this for a time no answer at all was given. It was 
not till the snails had been tried sixty to one hundred 
and ten times that they began to answer, but after 
the Rubicon was crossed they answered back all 
the rest of the total of two hundred and fifty trials. 
It was noteworthy, however, that the number of 
mouth-movements in a single response did not 
reach so high an average as was exhibited when the 
food stimulus was used by itself. The snails that 
gave the normal answer-back to the two stimuli 
applied simultaneously were regarded as “trained,” 
and were ready for the next and crucial step in the 
experiment. Forty-eight hours after the comple- 
tion of their training the snails were tried with the 
foot-pressure stimulus by itself. The dux of the 
class gave the proper mouth-moving answer the 
first seven trials right away; two other answers 
