AN ANALYSIS OF THE LEARNING PROCESS IN THE SNAIL 33 



12. The average duration of a single reaction in the normal 

 food-response is much more nearly the same in different indi- 

 viduals than is the number of reactions constituting a response. 

 This average in seconds for the six* snails in the order of paragraph 

 11 is, 1.29, 1.21, 1.3, 1.29, 1.39, 1.25. The values are obtained 

 by dividing the duration of the response in seconds (as obtained 

 with a stop watch) by the number of its component reactions. 

 At the above rate the number of reactions per minute for the 

 six snails would be 46.51, 45.9, 46.15, 46.51, 44.44, 48.0, or a 

 mean of 46.25 reactions per minute. 



13. An apparatus (food-pressure apparatus, fig. 1, Plate I) 

 was devised for the simultaneous application of two unlike 

 stimuli, food to the mouth and pressure to the foot at a fixed 

 distance from the mouth. 



14. Pressure response of untrained snails. — By means of the 

 food-pressure apparatus pressure was applied to the foot at a 

 fixed distance from the mouth. No stimulus was applied to 

 any other part of the animal. In one hundred twenty applica- 

 tions of pressure to six snails (20 each) but four responses were 

 obtained. Response thus occurred to C).^>^yc of the applications 

 of pressure. The responses were probably due to chance stimu- 

 lation by mucus. Response to pressure on the foot with the 

 apparatus used occurs in so small a per cent of cases that it 

 does not affect the experiments summarized below. 



15. Food-pressure response. — When food was applied to the 

 mouth and pressure to the foot at the same instant no response 

 followed in the first 60 to 110 trials, in six series of 250 trials 

 each (Snails 4, 5, 6, 7, 8 and 14). Response followed in the 

 remaining trials of each series. In a total of 376 responses for 

 the six snails, the average number of reactions per response was 

 3.42 as compared with 5.86 with the same snails when the food 

 stimulus alone was used (Tables III and VI-B, pp. 13 and 30). 

 The snails are referred to as " trained." 



16. Pressure response of trained snails. — Forty-eight hours 

 after the completion of their training, pressure alone was applied 

 to the foot of the six trained snails (paragraph 15). In the 

 case of Snail No. 4 response followed the first nine trials. The 

 last two of these were separated by an interval of 48 hours from 

 the first seven. The effect of training thus persisted for 96 



