AN ANALYSIS OF THE LEARNING PROCESS IN THE SNAIL 35 



22. The average number of reactions per response resulting 

 from the appHcation of pressure alone to the foot of trained 

 snails (paragraph 16) is greater than the average number result- 

 ing from the application of either food or food-pressure stimula- 

 tion. The numbers for the six snails in their numerical order is 

 1.25, 4.0, 4.92, 6.09, 8.0, 3.8, or a mean of 4.67 reactions per 

 response. These averages differ more than those of either food 

 or food-pressure responses (Tables II, III and VI-A and VI-B, 

 pp. 8, 13 and 30). 



23. The average duration of the reactions resulting from the 

 pressure stimulus alone on the foot of the trained snails is less 

 than that of the normal food response. This is shown by the 

 average number of reactions per minute for the six snails, 53.9, 

 which is 7.65 more than with the normal food response (Tables 

 IV and VI-C, pp. 25 and 31). In all trials the -reaction duration 

 is notably constant. 



6. Discussion 



A. Method. — The experimental method used in this research 

 will be called the method of training by the use of simultaneous 

 stimuli. The term may be applied to any procedure in which 

 two unlike stimuli are applied together or in immediate succes- 

 sion, to one of which the animal has previously responded by 

 a definite reflex, but to the other of which it has failed to respond 

 b}^ the same reflex. The purpose is to establish response to 

 the second stimulus alone. The stimuli may be referred to as 

 prim_ary and secondary and the primary stimulus may be called 

 " conditioned " when used with the secondary (Pawlow's terms). 

 The term, as thus defined, includes the salivary reflex method 

 of Pawlow. 



Comparison of the method with the salivary reflex method. The 

 Pawlow^ method has been described (p. 2). It requires that the 

 responses to the primary stimulus be a reflex, a so-called involun- 

 tary response, and that it be measurable. In order to meet the 

 first requirement the response must, (a) occur only in response 

 to external stimulation, (b) " always " occur in response to exter- 

 nal stimulation; that is, it should occur with sufficient regu- 

 larit}^ to be available for experimental uses. 



That the mouth response of Physa occurs only in response 

 to stimulation of the mouth region has been shown. In six 

 animals carefully guarded from such stimulation for a total 



