i 4 ANIMALS AT WORK AND PL A Y 



lightly or heavily at will. Nothing can be more 

 slow, reluctant and leisurely than the enforced wak- 

 ing of a petted house-dog when it does not wish 

 to be disturbed. It will remain deaf to a call, 

 twitch its feet if tickled, but not unclose its eyes, 

 and finally stretch and yawn like a sleepy child. But 

 mention something interesting to the same dog when 

 sleeping, such as the word ' walk,' or click the lock 

 of a gun, and it is on its feet in an instant, and 

 ready for enterprise. Thus animals seem capable of 

 three forms or degrees of sleep one, the deep stupor 

 of the nocturnal creatures ; a second, the semi-human 

 slumber of carnivorous and domesticated animals, 

 which have a power of vigilance at command ; and 

 lastly, the vigilant sleep of the persecuted ruminant 

 and rodent tribes. The highly - sensitive sleep of 

 the last is probably a development from natural 

 causes. Even human sleep can be made vigilant 

 by solicitude or previous resolve. It is a common 

 experience that persons who are heavy sleepers can 

 awaken at a certain hour by resolving to do so, or, 

 if roused by a sound previously agreed on, recognise 

 it as a call to awaken and do awaken instantly. In 

 cases of sickness the least movement of the patient 

 will arouse an anxious nurse who sleeps ; and in 

 sleep itself the brain often exercises a curious vigil- 

 ance, for it recognises in dreams forgotten sensations 



