Slonaker, Activity of the Rat. 



355 



cannon, etc., in celebrating independence day. This may have 

 had some effect in retarding their activity. Or on the second 

 night the rats may have become somewhat accustomed to the 

 hght from their former experience and were reasonably active in 

 spite of it. 



From this only one conclusion can be drawn; that is, light does 

 seem to have an influence on the time of the rat's activity. The 

 wild gray rat has by natural selection become accustomed to seek 

 its food at night to escape its enemies. Its various organs have 

 been modified to fit it for this nocturnal habit. The most promi- 

 nent organ that has been changed is the eye. The very large pupil 

 and the great predominance of rods in the retina fit it especially 

 for perceiving objects in dim and diffuse light. Bright light would 

 not only be blinding but very probably painful. In the white rat^ 

 owing to the absence of pigment in the eye, this effect of light would 

 be more marked. This I think is the most instrumental cause 

 for the nocturnal activity in the white rat. 



TABLE IV. 



Representing the number of revolutions of the revolving cages during tiie nighttime and the daytime 

 of a number of days. The lights were left burning during the entire night on July 4 and 7 to determine 

 what effect light would have on the activity. 



Date. 



June 25 

 26 



27 

 28 

 29 



30 

 July I 



In order to show more clearly the actual difference in activity 

 between day and night work Table IV has been constructed. 



