AN ANALYSIS OF THE LEARNING PROCESS IN THE SNAIL 61 



therefore feel the difference between a rough and smooth path. 

 4. For the failure-to-get-air punishment with the U-shaped 

 labyrinth there was substituted the electric shock. Reward 

 was the getting of air. 



The problem resolved itself then, into an attempt to determine 

 whether or not the snail could form a simple association between 

 two dissimilar stimuli one of which (punishment) followed the 

 other (warning). It has already been shown that the snail can 

 form a weak association between two stimuli simultaneously 

 applied (food-pressure series). Can it then bridge over an 

 interval between two stimuli one of which follows the other 

 almost immediately!* 



Glass tubing, 5 mm. in diameter, in the form of a Y was used. 

 One arm of the Y, 4.5 cm. in length, reached the surface of the 

 water. The other arm, 3.5 cm. in length, was short enough so 

 that the animals could not reach the surface. The stem of the 

 Y was 3 cm. long. Two (No. 23) silk-insulated copper wires 

 were passed through the stem to the upper end of the short 

 arm, where they connected with two fine platinum wire (No. 26) 

 rings passing around the end of the short arm close enough 

 together so that an electric current could be passed between 

 them, when proper connections were made. The upper ends 

 of both arms were then closed w4th sealing wax to keep out 

 the water. A hollow base, 4 cm. by 2 cm. by 1.5 cm., of lead 

 was made, in order to permit an outlet for the wires. These 

 passed from the lower end of the stem of the Y into a rubber 

 tube which carried them, protected from the water, through 

 the metal base, along the floor of the experimental tank and 

 upward to the outside. A direct current of 0.2 amperes was 

 taken from 220 volt mains through a lamp of 1100 ohms in 

 series with S ohms of other resistance. From the terminals of 

 8 ohms a second circuit was taken including a rheostat of 1800 

 ohms, a receiving switch, a key and the Y apparatus. When 

 no current was drawn through this second circuit the voltage 

 between the two platinum wires would be 1.6 volts. The 

 maximum current which could be drawn through the circuit 

 by short-circuiting the two platinum wires was slightly less 

 (actually 16-18) than 0.001 amperes or 1 milliampere*. It was 



*The author is indebted to Professor A. W. Smith for measuring the electric 

 current used in the experiments. 



