24 JAMES ROLLIN SLONAKEB 



activity at the ages indicated, one can get a good idea of the 

 nature of their activity. Fig. i represents their activity at 

 the age of 32 days, or four days after they had been weaned 

 and placed in the revolving cages. As can be readily seen the 

 periods of continuous running are of very short duration. Also 

 the periods of activity and rest have no definite arrangement 

 with respect to the hours of the day. The longest period of 

 continuous rest is about six hours and the longest period of 

 continuous activity lasts but a few minutes. This result was 

 no doubt due to the fact that at this age the young are accus- 

 tomed to feeding at frequent intervals. Since the rats could 

 not go from their nests to the food without jumping on to the 

 revolving cage they left their graphic records each time they 

 passed from the nest box. But one must not infer that each 

 graphic record represents a feeding time. Numerous observa- 

 tions proved that they revolved the cages many times without 

 going near their food. 



Fig. 2 is the graphic record at the age of six months. This 

 shows some marked changes. Though they still show a more 

 or less restless disposition throughout the 24 hours the main 

 part of their activity is confined to the hours between 7 p. m. 

 and 3 a. m. During these hours they ran almost continuously 

 fc periods of 30 or 40 minutes at a time. The records are 

 slightly misleading in this respect. The kymograph paper moved 

 so slowly that intervals of two or three minutes could occur 

 without a break or space showing in the record. A solid block 

 on the record, therefore, does not necessarily mean that a rat 

 has run continuously without a single stop for the time indicated. 

 The longest period of continuous running without a single stop 

 which was observed was between four and five minutes. During 

 this time they would often turn the cage at the rate of a hundred 

 or more revolutions per minute. After a rest of a minute or 

 so they would again run for a number of minutes. The record 

 of activity would thus appear to be continuous so long as the 

 interval of rest was not longer than about two minutes. 



The very intermittent and irregular activity seen from 1 1 

 a. m. to 7 p. m. is easily explained. They were accustomed to 

 being fed between 3 and 5 p. m. At this age they were more or 

 less restless for an hour or so before feeding. After feeding 

 they carried all they could conveniently into their nest boxes. 



