12 HELEN B. HUBBERT 



the time set, it was not considered perfect. For the purposes 

 of this experiment such a norm was not desirable, since one of 

 the points under investigation was the relative final rate of 

 efficiency attainable by rats of different ages. Elimination of all 

 useless movements for three days was therefore considered as 

 sufficient evidence that the problem had been learned. The 

 number of trials required to reach this level of efficiency varied 

 with each rat, the extreme limits being fourteen and one hun- 

 dred twelve trials. In a single trial any distance greater than 

 four and five tenths meters, which is the length of the errorless 

 pathway from the entrance to the food, represents excess effort 

 on the part of the animal. 



If a rat remained in the maze for fifteen minutes without 

 reaching the food box he was taken out and replaced in the 

 entrance box for a second attempt. Distance and time were 

 recorded in the same way as for a successful run, i. e., if the 

 first effort to reach the food proved unavailing after fifteen 

 minutes, and the second attempt was successful after eight 

 minutes, the total time for the first trial would be twenty-three 

 minutes and the total distance the combined distance of the two 

 attempts. Should the rat fail on the second effort also, it was 

 fed for three minutes in the maze with the food box partitioned 

 off as for preliminary feeding, and tried again the following day. 



The time and distance records for each trip were carefully 

 tabulated, and form the basis for the conclusions which appear 

 later. In many cases the actual tracings were kept for reference. 



EXPERIMENTAL RESULTS 



It was planned to work with five groups of rats, twenty-five, 

 sixty -five, two hundred, three hundred and five hundred days 

 old respectively, since it was thought that these ages represented 

 fairly well the successive stages in the growth and development 

 of the animal; twenty-five days for youth, sixty-five days for 

 sexual maturity, two hundred days for maturity, three hundred 

 days for age, and five hundred days for old age. The attempt 

 was made to have thirty rats in each group, but sickness and 

 unavoidable accidents among the animals have brought the 

 number somewhat lower. It has been found extremely difficult 

 to obtain rats for the last group (500 days). Although Slonaker 

 finds the average length of life of the white rat to be thirty-four 



