r 50 Traces of Unity in the 



The devitalizing action of cold and darkness upon 

 animal bodies is not to be questioned ; and, as in the 

 case of plants so in this case, the vital vigour is always 

 directly proportionate to the degree of insolation to 

 Avhich these bodies are exposed. 



The fact, too, that animals for the most part wake in 

 the daytime and sleep during the night, is not a little 

 significant when taken in connection with the context, 

 It is not enough to refer the state of sleep to the exhaus- 

 tion consequent upon the state of wakefulness, or to 

 think that wakefulness follows upon sleep because the 

 body has been refreshed by sleep. If it were so the 

 shortest day would not be followed by the longest sleep, 

 and the longest day by the shortest sleep. If it were so, 

 that is to say, the times of repair in sleep and of waste 

 in waking would not be, as they are, inversely related to 

 each other. Indeed, the more this matter is looked into 

 the more difficult is it to regard the sleeping and waking 

 states as standing to each other in the relation of cause 

 and effect, and the more easy it becomes to entertain the 

 belief that sleeping and waking, like hybernation and 

 aestivation, have to do directly with the absence and 

 presence of the sun, and that, for this reason, the varying 

 periods of sleeping and waking in winter and summer 

 must in great measure keep strict time with the changes 

 in the length of the nights and days in these seasons. 

 Nor is this conclusion set aside by the fact that some 

 animals, like the bat, wake when others sleep, for in the 

 daytime these nocturnal creatures hide themselves in 

 dark places where night may be said to prevail even 

 during the day. Indeed, after all, these nocturnal 

 creatures may differ from diurnal creatures chiefly in 

 sleeping, not only through the day, but through the 

 greater part of the night also, and in coming abroad only 





