286 ADA W. YERKES 



One of the inbred females had died just before these tests were 

 given, but of the seven remaining everyone gave evidence of 

 perfect memory of the habit. 



It will be noticed that in the tables for group 1 the records 

 are somewhat irregular owing to the variety of experimenters 

 and to lack of time. It seems worth while to present them, 

 however, as far as they go. The tests under condition 1 were 

 carried out to twenty perfect trials in succession and then in 

 some cases review series were given. The latter are not in- 

 cluded in the figures given in table 9. Discrimination under 

 condition 2 with these rats was in no case carried out to the 

 same limit, but it will be. noted that even where fifty trials 

 were given, the animals had not succeeded in attaining this 

 standard. It is possible that under these easy conditions of 

 discrimination further training might have ended in perfect 

 discrimination. Observation showed, however, that punish- 

 ment following repeated errors made the rats both timid and 

 reckless, and the increasing difficulty of working with animals 

 who were frightened, sulky, and careless made it inadvisable to 

 carry discrimination further than condition 3 except in a few 

 trial cases. 



The results in these tables present the following facts. (1) 



There was shown a decided preference by all the rats for the 



dark box. 



Preference Series 



Light Dark 



Group 1 Stock 54 59 



Inbred 52 67 



Total 106 126 



Group 2 Stock 36 44 



Inbred 30 50 



Total 66 94 



This preference was more marked in the inbred than in the 

 stock rats for the latter of both groups chose the dark 103 times, 

 the former chose it 117 times. 



(2) Of the twelve rats of Group 1 only one succeeded in 

 making a perfect record (20 correct trials) under condition 3. 

 Of the four rats which were tested further than this two showed 

 evidence of discrimination under condition 4 but they were not 

 allowed to carry the experiment far enough to secure a perfect 



