16 



HELEN B. HUBBERT 



Twenty-seven rats were experimented with at this age, eleven 

 males and sixteen females, eight strains being represented as 

 follows : 



The first letter indicates the father, the second letter the 

 mother, of the litter. Individual rats were distinguishable from 

 each other by a convenient system of ear marks, and on every 

 cage was a tag showing the experimental number, parentage, 

 date of birth, sex and ear mark for each rat contained therein. 

 Thus, W M 1/9/14 R 9 4, would be deciphered, rat number 

 four, female, right ear straight, born January ninth, 1914, 

 mother M, father W. 



The number of trials required by animals of this group in 

 learning the problem varied from fourteen to fifty-one, the 

 absolute time from four and nine-tenths seconds to nine and 

 one-tenth seconds, the total time from sixty-four minutes to 

 six hundred forty-nine minutes ; and the total distance from one 

 hundred thirty-nine meters to four hundred eighteen meters. 



The " absolute time " is the average time for the last six 

 trials, represents the limit of efficiency in speed for a given 

 group, and varies among individual rats within the group as 

 well as for the groups themselves. Thus, the record time for 

 the twenty-five day group was made by a rat which could run 

 from entrance to food box in four seconds, but no other rat 

 attained this speed, and one in particular could not make the 

 run in less than eight seconds. The last six trials were all with- 

 out error and would seem to afford a fair basis for judging the 

 average final efficiency, which for this group was five and seven- 

 tenths seconds. The absolute distance is the same for each 

 group, since the last six trials are errorless, and the true pathway 

 measures approximately four and five- tenths meters. 



