in ON ANIMAL LIFE 79 



moderates heat, the coin that purchases all 

 things, the balance and weight that equals the 

 shepherd with the king, and the simple with 

 the wise." Some animals dream as we do ; 

 Dogs, for instance, evidently dream of the 

 chase. With the lower animals which cannot 

 shut their eyes it is, however, more difficult 

 to make sure whether they are awake or 

 asleep. I have often noticed insects at night, 

 even when it was warm and light, behave 

 just as if they were asleep, and take no notice 

 of objects which would certainly have startled 

 them in the day. The same thing has also 

 been observed in the case of fish. 



But why should we sleep ? What a remark- 

 able thing it is that one-third of our life should 

 be passed in unconsciousness. "Half of our 

 days," says Sir T. Browne, " we pass in the 

 shadow of the earth, and the brother of death 

 extracteth a third part of our lives." The 

 obvious suggestion is that we require rest. 

 But this does not fully meet the case. In 

 sleep the mind is still awake, and lives a life 

 of its own : our thoughts wander, uncon- 

 trolled, by the will. The mind, therefore, is 



