HABIT FORMATION IN ALBINO RATS 15 



inbred rats used in this experiment. Two of the 7th generation 

 failed to learn the maze; all the 6th generation had learned it 

 after eighty-three days. The 6th generation required, on the 

 average, 32.93 days in which to learn; the 7th generation, 44.00 + 

 days. The absolute retention of the 6th generation was, on the 

 average, 65.443 seconds; of the 7th generation, 126.680 seconds. 

 Two of the 6th generation failed to relearn; all the 7th genera- 

 tion had relearned at the end of fourteen days. The 6th genera- 

 tion required, on the average, 14.14+ days to relearn; the 7th 

 generation but 8.60 days. 



In these criteria of ability, the 6th generation excelled in 

 learning and absolute retention; the 7th in relearning. It must 

 be remembered, however, that the 7th generation rats used in 

 the relearning test formed a selected group, the two rats having 

 failed to learn having been from this generation. On the whole, 

 the ability of the 7th generation inbreds in the maze experiment 

 appears to be somewhat inferior to that of the 6th generation. 



The body length and body weight of the 6th generation aver- 

 age greater than those of the 7 th. The average actual brain 

 weight of the 6th generation is greater than that of the 7 th. 

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

 6th generation is -.91% less than that of the 7th generation. 

 The relative brain weight (in reference to body weight) of the 

 6th generation is 1.50% less than that of the 7th generation. 

 The relative brain weight of the inbred rats used in the maze 

 has not decreased from one generation to the next; but all the 

 7th generation rats were females, and the females normally 

 have relatively greater brain weights than the males. The 

 percentage of water in brain and cord is within .03% of the 

 same figure in the two generations. 



TABLE Ila 



The Maze 



Daily Learning Averages of Sixth and Seventh Generation Inbred Rats 



(Time in seconds) 



Day 1 Day 2 Day 3 Day 4 Day 5 



Sixth Average 541.423 73.343 79.997 37.449 30.014 



Seventh Average 512 . 149 127 . 526 44 . 486 43 . 480 16 . 674 



Day 6 Day 7 Day 8 Day 9 Day 10 



Sixth Average 24.457 16.371 10.646 10.486 9.789 



Seventh Average 11.131 8.954 11.891 8.154 8.989 



