ANIMAL SLEEP 



THOUGH many animals look on sleep as a luxury, and 

 make comfortable beds for its enjoyment, others sleep 

 but little ; and their slumbers are so light, that they 

 seem to have the power of becoming instantaneously 

 awake, however soundly they may have been sleeping. 

 It is commonly said of some creatures that they ' sleep 

 with one eye open/ The instantaneous transition by 

 which, when wakened, they pass into action, such as 

 flight and escape, with full possession of their faculties, 

 almost suggests that they have some additional sense, 

 which takes the form of vigilance in sleep, and remains 

 conscious when all other consciousness is lost. This 

 is an easy, but not a satisfactory, explanation of this 

 quick recovery of sense by sleeping animals ; for it 

 attributes to them a faculty not possessed by man, 

 under conditions in which the life of men and animals 

 would naturally be supposed to differ least that is, 

 when the use of their higher faculties is for a time 

 partially suspended. 



