HABIT FORMATION IN ALBINO RATS 



33 



the inbreds had relearned at the end of the twenty-fourth day; 

 but all the controls had relearned at the end of the seventeenth 

 day. The inbred rats required, on the average, 6.74 days to re- 

 learn; the controls but 4.68 days. 



In all these criteria of ability, learning, absolute retention and 

 relearning, the rats of the normal control series are shown, on 

 the average, to be superior to those of the inbred series. 



The body length of the inbred rats used in the inclined plane 

 experiment is, on the average, a trifle greater than that of the 

 controls; the body weight is slightly less. The average actual 

 brain weight of the inbreds is less than that of the controls. The 

 relative brain weight (in reference to body length) of the inbreds 

 is 5.89% less than that of the controls. The relative brain weight 

 (in reference to body weight) of the inbreds is 2.38% less than that 

 of the controls. Although the inbred rats were killed, on the 

 average, at a more advanced age than the normal controls, the 

 percentage of water in brain and cord is higher. 



The figures presented in Table V support the hypothesis that a 

 less than normal average brain weight in a strain of rats is ac- 

 companied by an average lesser ability to form habits. 



TABLE Va 

 THE INCLINED PLANE 

 DAILY LEARNING AVERAGES OF INBRED AND NORMAL CONTROL RATS 



Inbred Average . . 

 Control Average. 



Inbred Average 



Control Average 



Inbred Average . . 

 Control Average . 



Inbred Average 



Control Average 



Inbred Average . 

 Control Average. 



Inbred Average . 

 Control Average. 



