12 GARDNER CHENEY BASSET 



In Plate II is shown the curve of learning (below) and of 

 relearning (above) of the inbred rats compared with those of 

 the normal control. These curves are constructed from figures 

 given in Table I. The curve of the inbred rats is indicated by 

 the solid line, that of the normal control by the broken line. 

 The ordinates give the average daily time in seconds for each 

 group, and the abscissae the number of the day in which such 

 time was made. The time required by both inbred and control 

 rats 'for the first four days was so long that it is represented 

 here by figures and does not appear in the curve. For the first 

 few days the descent in time for both the inbreds and the con- 

 trol is very rapid. From the twentieth day the curve of the 

 control rats lies entirely below the six-second mark. The curve 

 of the inbred rats never reaches even an approximately flattened 

 appearance, but exhibits great irregularities, particularly on the 

 forty-fifth, sixty-first, eighty-second, ninetieth and ninety- 

 second days. The inbreds' curve of relearning is more similar 

 to that of the controls, but it must be borne in mind that the 

 two inbreds and one control rat that failed to learn the maze 

 are not represented in the relearning curve, and for this reason 

 this curve applies to selected groups. From the twenty-second 

 day the control curve of relearning is perfectly flat at 5.3 seconds, 

 all the control rats having relearned. Two of the inbred rats 

 having failed to relearn, their curve of relearning remains slightly 

 irregular and above that of the control in time. 



In Plate III may be seen the curves representing the distri- 

 bution of learning and relearning of both inbreds and control 

 for the maze experiment. The time is given in days in groups 

 of five for learning, in groups of two for relearning. As may 

 readily be seen, the advantage from the standpoint of time 

 (days required to learn and relearn) lies wholly in favor of 

 the normal control group. 



The question arises as to whether the later generations of 

 inbred rats differ from the earlier in the ability to form habits; 

 that is, is decrease in this ability progressive even if, as earlier 

 stated, decrease in relative brain weight after the 4th genera- 

 tion is not. Of the inbred rats used in the maze experiment, 

 fourteen were from the 6th generation and seven from the 7th 

 generation. In Table II is presented a comparative summary 

 consisting of the daily averages of the 6th and 7th generation 



