of the (-13), but 51,083 seconds. Two of the inbreds fuiTed to 

 relearn; all the B haa relearncd at the end of the twenty-sec- 

 ond day; while all the ( -L ) had rel earned at the end of the 

 eighth day. The inbreda required, on the average, 12.68- days 

 to relearn; the B, 8.24 days; the (-E), but 4.08 days. 



In these criteria of ability the inhreds did the 

 lepst well; the 3 rnts were, in each instance, not far from 

 their record; the (-3) were nuch superior to either. 



3oth body lentith and body weight were e^reatest in 

 the inbreds, next in the B, and least in the (-B). Actual brain 

 weight was lenst in the inbreds, much greater in the 3, and 

 slightly greater in the (-3) than in the 3. The relative brain 

 weii:ht (in reference to body length) of the inbreds *as 5.46;^ 

 less than that of the (-5); that of the 3 was 2.53^^ less than 

 that of the (-3). The relative brain weight (in reference to 

 body v/eight) of the inbreds was 10. 02,^ less than that of the 

 (-3); that of the 3 was 5.15> less than that of the (-3). As 

 might be expectea from the behavior and the hypothesis, the 

 average relative brain weight of the 3 strain lies between 

 that of the inbreds end of the (-3). 



The results here obtained reinforce the former con- 

 clusion that deterioration of brain v/eight in a strain of rats 

 is accompanied to a similar degree by deterioration in the 

 ability to form habits. 



In Plate V is shovm the curve of learning (belov/) 

 and of relearning (above) of the inbred -ind 3 rats compared 

 with those of the (-3). The inured curve is represented by 

 the solid line, the 3 by the heavy broken, and the (-3) by 

 the lighter broken line. The oruinates ^^ive the average time 

 in seconds, and the abscissae the nuiiber of the day in whicli 

 such time was made. From the tv/entieth aay the (-3) curve is 



