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 

 (Time in seconds) 



Day 1 Day 2 Day .3 Day 4 Day 5 



Inbred Average 4673.131 1218.976 166.997 56.576 22.926 



Control Average 2769 . 953 1072 . 722 133 . 287 61 . 600 23 . 995 



Day 6 Day 7 Day 8 Day 9 Day 10 



Inbred Average 36.878 12.422 11.061 10.751 8.136 



Control Average 25,874 13.478 11.704 11.280 6.961 



Day 11 Day 12 Day 1.'? Day 14 Day 15 



Inbred Average 9.383 7.876 8.625 7.188 9.586 



Control Average 6.759 6.858 6.347 7.045 6.383 



Day 16 Day 17 Day 18 Day 19 Day 20 



Inbred Average 8.710 8.069 7.364 9,191 6.717 



Control Average 5,069 5.400 6.158 5,376 5.352 



Day 21 Day 22 Day 23 Day 24 Day 25 



Inbred Average 6.919 6.363 6.951 6,458 7,329 



Control Average 5,284 4,378 5,173 5,280 5.025 



Day 26 Day 27 Day 28 Day 29 Day ,30 



Inbred Average 5,674 6.262 6.627 5.514 27,802 



Control Average 4,978 5,139 5.276 4.302 4,303 



