30 WALTER S. HUNTER 



centage of coiTect reactions to be required of all animals. As 

 will be seen in the following experiments some animals were 

 advanced from stage to stage when but 70% of correct reactions 

 were made. Others were detained on one stage until 85% or 

 95% were made. Sometimes an animal was given 5 or 10 trials, 

 sometimes 150 or 200 trials on one stage of delay. One general 

 fact, however, should be noted: The first set of rats, Bob and 

 Betty during their first year's work, and H, L, M, and Hd of the 

 children were rushed from stage to stage as fast as was at all 

 feasible. The emphasis here lay upon what the subjects could 

 do with their native equipment. With the other subjects used 

 and with Bob and Betty during the second year's work, a larger 

 number of trials were given on each stage of delay and the 

 advance in the length of the periods was more gradual. The 

 emphasis here was placed on what the subjects could learn to do. 



V. EXPERIMENTAL RESULTS 



1. Tests with Animals 



A. Learning the Association, (a) Rats. — The method of ex- 

 perimentation used by Hough and 'Reed was retested with the 

 result that the general method outlined above was adopted. 

 These tests were made upon five normal adult rats, Nos. 18-22. 



The regular experiments may be divided into two sets: (A) 

 Those in which reward only was employed; and (B) those in 

 which both punishment and reward were used. Nine rats, 

 Nos. 1-9 were tested in the first set and eight, Nos. 10-17, in 

 the second set. Of the rats in A, Nos. i, 3 and 8 were in poor 

 health, and their records will not be considered. 



Table I gives the number of trials required by the rats of 



Set A to learn the association between the light and getting 



food. These rats were given 5 trials daily. All save No. 6 



learned the association. Of the last 50 trials given this animal, 



only 40% were successful; while of the entire 800, 54% were 



correct. 



TABLE I 



