44 HELEN B. HUBBERT 



the maze habit more quickly than those three hundred 

 days old. 



The speed (which it will be remembered is the average num- 

 ber of centimeters run per second throughout the learning pro- 

 cess, no distinction being made between early and late trials) 

 without exception decreases with increased age. The last group 

 is distinctly slower than any other and this to our mind is again 

 proof of the lessening of activity with age. 



The absolute time, which we have taken as the indication 

 of final efficiency, also diminished with increasing age, and is 

 considerably lower at three hundred days than at any previous 

 age. Thus, while at twenty-five days the average length of 

 time required for the execution of a perfect run was five and 

 seven tenths seconds, at three hundred days the very best time 

 in which the food could be reached was eleven and six tenths 

 seconds, more than twice the time of the youngest group. It 

 follows -that in the formation of habits in which the factor of 

 speed is of an importance, equal to or greater than that of ex- 

 actness, the older animals would be considerably handicapped. 

 In the field of animal experimentation illustrations of habits 

 where speed is an important factor are difficult to find. On 

 the human side such an illustration might be had in the ac- 

 quiring of technique in piano playing or voice culture, either 

 of which demands the rapid succession of the muscular activ- 

 ities involved in rendering scales, arpeggios, trills, etc. It would 

 seem that habits requiring extreme rapidity of execution within 

 a prescribed rhythm could not be learned by the older animals. 



A comparison of the relation of distance to time in the younger 

 and older groups is interesting. In the first two groups the 

 distance is relatively high* showing the excess activity displayed 

 by the younger animals, in the two hundred day group it is 

 about the same as the time, indicating that excess activity is 

 at a minimum, while in the last group it is much less than the 

 time, showing that the effects of old age have begun to manifest 

 themselves through a general slowing up of activity. 



If the distance alone be taken as a measure of activity, our 

 results agree with those of Slonaker who found the most active 

 age to be between ten and twelve and a half months, since our 

 three hundred day rats covered more distance in learning the 

 problem than any other group. If, however, distance be con- 



