HABIT FORMATION IN ALBINO RATS 45 



worked one hundred days (500 trials). At the expiration of 

 sixty days after perfect learning the rats, except those failing to 

 learn, were tested for absolute retention and relearning until 

 relearning was perfect, or, failing relearning, for fifty days (250 

 trials). 



2. The Preliminary Inclined Plane, in which all the rats used 

 were given five trials daily for twenty days (100 trials); at the 

 expiration of sixty days after this period they were all tested for 

 absolute retention and relearning for a period of five days (25 

 trials). 



3. The Inclined Plane, in which all the rats used were given 

 three trials daily until they had learned perfectly, or, failing to 

 learn, had worked one hundred days (300 trials). At the ex- 

 piration of sixty days after perfect learning the rats, except those 

 failing to learn, were tested for absolute retention and relearning 

 until relearning was perfect. 



In all these experiments the strain of rats of lesser relative 

 brain weight (the inbreds) learned less well, on the average, than 

 the normal control series. In the maze and inclined plane ex- 

 periments the average number of days required to learn and re- 

 learn, and the time of absolute retention, was far greater in the 

 case of the inbred rats than in that of the normal control series. 

 In the maze experiment, two inbreds and one control failed to 

 learn; two inbreds failed to relearn. In the inclined plane ex- 

 periment, eleven inbreds and two controls failed to learn. 



The similarity of behavior of the control rats containing blood 

 of the B strain to that of the inbreds suggests the importance 

 of crossing a strain of inbred rats of lesser brain weight with normal 

 rats, and carrying out a series of tests such as have been presented 

 in this paper, with two controls : one of normal rats, and one of 

 rats of lesser relative brain weight. 



In the maze experiment the inbred rats of the seventh genera- 

 tion did a little less well than those of the sixth. In the inclined 

 plane experiment the rats of the eighth generation did a little 

 less well than those of the seventh. It would seem (although 

 lessening of relative brain weight had ceased after the fourth 

 generation of inbreds) that the ability to form habits lessened pro- 

 gressively with successive generations of inbreeding. 



The writer had intended to attempt a correlation (if any 

 existed) between the number of days required to learn a habit 



