INTERFERENCE OF HABITS IN THE WHITE RAT 55 



though kept in good physical condition, for the following inter- 

 vals of time: Nos. 1 and 11 went 10 days; No. 17 went 23 days; 

 and No. 18 went 40 days. At the close of these intervals of 

 time, all of the rats were brought back to the standard percent- 

 age of correct reactions on turning to the right for handclaps. 

 They were then put into training again on going right for 256 

 d. v. and left for silence. They remained in this series for 600 

 trials, 10 per day, punishment and reward. No. 11 was the 

 only rat of the four that improved during the 60 days. He 

 learned the reaction in 270 trials. The senior author was away 

 for the summer at this time and no control tests were made to 

 determine the basis of the response. Inasmuch, however, as 

 no other rat in the laboratory has learned to react to tone in 

 this fashion since the work was begun in 1913, and inasmuch as 

 this rat learned rapidly, it is most probable that the reaction 

 was due to secondary cues accompanying the tone. This ex- 

 periment is confirmatory of work previously published indicat- 

 ing the insensitivity of the rat to certain tones. 



At the close of the 600 trials, retention tests for handclaps 

 to the right were given. No. 1 came back to standard in 10 

 trials; No. 17, in 60; and No. 18, in 30. This is practically 

 perfect retention and is as good a record as that made by the 

 30-day rats. The results are practically comparable, although 

 not absolutely so inasmuch as the 60-day animals were some- 

 what overtrained relatively on h. c. to the right. 



The same results with the same limitations were secured with 

 rats 4, 8, 22 and 24. These were the rats listed under F in 

 the 30-day tests. The retention tests in that series brought 

 these animals back to the standard. They were then idle for 

 60 days at the close of which period they were again retested 

 on h. c. to the right. Rat No. 4 came back to standard in 

 20 trials; No. 8, immediately; No. 22, in 30 trials; and No. 24, 

 in 40. In order to compare the results given here and in the 

 above paragraph with those listed under ' ' Total trials on re- 

 learning " in table 3, it is necessary to subtract 40 from each 

 of the totals in that table. The results given in the present sec- 

 tion are the number of trials up to the 40 made at the standard 

 per cent. 



Rats Nos. 7, 15 and 23 had been through the 30-day tests 

 in set B, — turn left for the buzzer. After intervals of rest as 



