ACTIVITY OF THE ALBINO RAT 25 



On this day they were fed at 3:20 p. m. It is noticeable that 

 at this age they had become much more regular in their habits 

 and, having become thoroughly accustomed to their surround- 

 ings, did not manifest the investigating nature which was so 

 prominent when they were younger. The playfulness which 

 was so conspicuous at an early age was less marked. 



In Fig. 3 is seen the record of their activity at the age of 

 11 months. It is now noticed that the activity begins mainly 

 with the feeding time (4 o'clock) and is practically complete 

 at 4 a. m. Activity and rest are thus divided into two almost 

 equal periods of 12 hours each. The period of activity being 

 confined mainly to early twilight and night and that of rest 

 to day time. Playfulness in action was not manifest at this age. 



At the age of 16 months very little change is to be noted in 

 the general activity (Fig. 4). A week previous to this record 

 the feeding time was changed to the morning to determine 

 what effect this would have on the distribution of their activity. 

 As is readily seen the usual random running found to generally 

 follow the feeding shifts to the morning, but the great bulk of 

 voluntary running occurs during the period of darkness and is 

 apparently in no way affected by the change in the time of 

 feeding. In other words the albino rat, like the wild Norway 

 rat, is nocturnal in its habits. 



Fig. 5 is the record of their activity when they were 2 1 months 

 old. At this age the rats were almost wholly inactive from 

 3 a. m. to 3 p. m. Their day was thus divided into two equal 

 periods of 12 hours each. Number 4 is beginning to show the 

 effects of old age as the periods of activity are of relatively 

 short duration and are separated by relatively long periods of 

 rest. Also this rat, though it has still done the greatest amount 

 of running during the night, has been more or less active through- 

 out the entire day. This is especially noticed in the records of 

 all at older ages. In other words, as the rats reach old age 

 their activity resembles more and more that of the very young 

 rat in distribution, but is less in amount. 



At the age of 25 months a marked diminution in the amount 

 of running is noticed (Fig. 6). It is now very obvious that 

 the female (No. 3) is much more active than the males (Nos. 

 1,2, and 4). The activity of each of the males is very similar 

 and shows the characteristic activity of rats in old age. Their 



