AN ANALYSIS OF THE LEARNING PROCESS IN THE SNAIL 11 



TABLE U— {Continued) 



Total number of trials 50 



Total number of stimuli followed by response 32 



Per cent of stimuli followed by response 64% 



Total number of reactions 139 



Average number of reactions per trial 2 . 78 



Average number of reactions in only those trials in which response 



occurred 4 . 35 



Total time of reactions 2.81 min. 



Average time per reaction 1.21 sec. 



Average number of reactions per minute 45 . 9 



Summary, Snails 4 and 5: 



Total number of stimuli (trials) 100 



Total number of stimuli followed by response 61 



Per cent of stimuli followed by response 61% 



Table II shows that when a food stimulus is applied to the 

 mouth region of Physa gyrina Say, response occurs in 61% of 

 100 trials with two snails. The individual records show that 

 the number of reactions making up the response varies from 1 

 to 38. The first 30 trials of the series of 50 trials for Snail 4 

 shows 67 reactions, while the following 20 trials give 3-4 reactions 

 with an average of 2.83 reactions per response. In the case 

 of Snail 5 the corresponding numbers are 43 and 96 reactions 

 with an average per response of i.i and 5.05. This indicates 

 in the case of Snail 5 a tendency to recover during the second 

 part of the series from the inhibiting effect of the manipulation 

 (adaptation). In Snail 4 the recovery may be delayed beyond 

 the limits of the series. The series is in both cases too short 

 to afford anything more than a suggestion as to the occurrence 

 of adaptation. The absence of reaction in certain trials and 

 the wide variation in their number in those trials in which they 

 occur and in the differences between individual snails, are brought 

 out in the summary (p. 31) and are discussed later. The average 

 number of reactions per response furnishes a means of comparison 

 of the results here obtained with those recorded in the part of 

 this paper which deals with the simultaneous use of two stimuli. 



4. Response to the Conditioned Food Stimulus: Simultaneous Appli- 

 cation OF Food and Pressure 



There are then determined the number of reactions of the mouth 



parts induced by a single definite stimulation and constituting 



a single response and the duration of the response and of the 



single reaction. The stiniulus according to Pawlow's terminology 



would be " unconditioned " or primary. An attempt vras next 



