50 WALTER S. HUNTER AND JOS. U. YARBROUGH 



C. 4 rats of set A train for 30 days to turn rt. for tuning 



fork 256 d. v. 



D. 4 rats of set A train for 30 days to turn 1ft. for tuning 



fork 256 d. v. 



E. 4 rats of set A train for 30 days on regular series of pre- 



sentations on auditory stimulus. 



F. 4 rats of set A tested for retention after 30 days rest. 



G. Rats of sets B, C, D, E retested on handicaps. 



This program calls for a measure of the relative retention of a 

 simple co-ordination in five groups of animals, each group having 

 been kept under different conditions for an interval of thirty 

 days. 



Only 18 rats completed the work of set A. Of these 13 were 

 females (numbers 1, 4, 9, 10, 11, 14, 15, 16, 18, 19, 20, 21, 24), 

 and 5 were females (numbers 7, 8, 17, 22, 23). All were about 

 three months old at the beginning of the tests. With the excep- 

 tion of nos. 1 and 4, they were untrained. No. 1 had been 

 trained on the inclined plane problem box. No. 4 had worked 

 with light in a two-choice discrimination box. Nos. a, b, c, 25, 

 26, 27, 28, 29, whose records are given below, were also about 

 three months old at the beginning of the tests. All of these 

 animals were females. The tests here reported, like most studies 

 of animal learning, have been long and tedious. They have ex- 

 tended from January, 1915, to June, 1916. 



Prior to the regular tests, each rat was fed on the experiment 

 table and was permitted to run through the box on each of two 

 days. Care was taken that no position habits were developed. 

 Those rats that manifested a preference for a certai n side of 

 the box were immediately forced through the opposite side. 



Discrimination was regarded as established when the average 

 percentage of correct reactions for four days together was 87|% 

 with no one day's record below 80%. 



II 



Learning the first habit. — Table 1 gives the total number of 

 trials required by each rat to set up the habit of running to the 

 right for handclaps and to the left for silence. The period of 

 learning is the period up to the 40 trials made at the standard 

 per cent. The rats underscored are males. Figure 1 shows 



