34 



HELEN B. HUBBERT 



They were fed in the maze for ten days before the beginning 

 of the problem, prehminary feeding being thus extended because 

 it was found that rats so old contracted digestive troubles unless 

 the decrease in food supply was made more gradual than for 

 the younger animals. They were allowed to eat for from six 

 to eight minutes instead of five, at the close of each day's work, 

 since they ate much slower than the younger rats, and could 

 not obtain sufficierit nourishment in the shorter time. These 

 rats differed markedly in behavior from those in any of the 

 preceding groups in that they were lethargic, inactive, and often 

 went to sleep in the maze instead of working at their problem. 

 A few of the animals of this group were from The Wistar Insti- 

 tute, and were somewhat timid and difficult to handle, but even 

 among animals bred in this laboratory the same disinclination 

 to work was noted, although with our own rats it did not last 

 so long. When the rats finally began to work, they went about 

 it differently from those of other groups. They were very de- 

 liberate, followed the culs de sac out to the bitter end whereas 

 the other rats often turned back toward the true path before 

 reaching the alley stop; furthermore, they did not hesitate to 

 enter the unexplored runways as did most of the other rats, 

 in this last respect resembling the twenty-five day rats. 



The trials varied from fourteen to eighty-four, absolute time 

 from five and eight tenths seconds to thirty-five and two tenths 

 seconds, total time from one hundred nine minutes to two 

 thousand two hundred seventy-four minutes, and total distance 

 from one hundred seventeen and three tenths meters to six 

 hundred nine and six tenths meters. 



