SECTION TWO 



GENERAL FEATURES OF THE EXPERIMENTS 



A. Animals Used. 



The animals were white rats of the same species as used 

 by Watson, Carr, Vincent, and others in work done in the 

 same laboratory in previous years. The rats were for the 

 most part young animals, beginning the work when some 

 three or four months old on the average. When young 

 animals were not used the fact will be found indicated in 

 the detailed reports of the experiments. In all, close to 

 one hundred and seventy-five animals were used. They 

 were divided into groups of five or six or seven to the group, 

 and the record for such a group was taken as representing 

 what the normal animal would do on the average under 

 like conditions. The food used was sunflower seeds. This 

 allowed better control of amount secured at each trial than 

 other types of food at hand. 



B. The Two Types — Positive and Negative 



Two series of experiments were planned and carried out. 

 In the first series the attempt was made to teach the ani- 

 mals a definite positive response to one sort of sense stimu- 

 lus. Then a second sort of stimulus was substituted for 

 the first. The purpose was to see whether and to what 

 extent such a response would carry over from the first to 

 the second. This series falls into two groups: (a) where 

 the response was first learned to the light stimulus, and 

 then the sound stimulus was substituted for the light; (b) 

 where the response was first learned to the sound stimulus, 

 and the light stimulus substituted for the sound. 



In the second series a negative response was required in 

 all cases. The purpose was the same as in the positive 

 series. This series falls into six groups: (a) where the 

 response was first learned to the light and the sound sub- 

 stituted, (b) where the response was first learned to the 



