222 Human Physiology. 



growth of the spirit requires a complete life, and all its 

 experiences from infancy to age. The only natural death 

 is that of the gradual decay of the body in old age. All 

 death from disease is unnatural death and premature mor- 

 tality. 



Among the phenomena of our bodily life, one of the most 

 remarkable is sleep. Young children sleep a large portion of 

 the time. Before birth, the whole life is probably a sleep, with 

 some disturbing dreams. Many animals sleep through the 

 winter months, taking little or no nourishment. The dormouse 

 and the bear alike sleep for months together, lying in a torpor, 

 which has we know not how much of sensation. Men sleep 

 from four to eight or ten hours out of the twenty-four. The 

 aged sleep less than the young. But we do not know why men 

 or animals require to sleep at all ; the heart never sleeps even 

 in hybernating animals. The lungs never sleep. The secre- 

 tions are kept up, as well as the circulation. The nervous 

 system of organic life never rests. Why should the nerves, or 

 any part of the nerves of animal life require the repose of sleep? 

 It has been thought that their alimentation requires it, but why 

 not the nerves, or the nervous centres that govern circulation 

 and respiration? What we know is, that long wakefulness is 

 very exhausting, and that a sleep of only five minutes' duration 

 wonderfully refreshes and invigorates us. The requirement of 

 much or little sleep, and the curious power wnich some persons 

 possess of measuring time in sleep, and waking up at any 

 moment fixed upon beforehand, may be classed with idiosyn- 

 crasies, impossible to explain. 



The sense of time may be an instinct, or intuitive faculty, like 

 the instincts of animals and insects. Savages have several 

 which seem almost lost to man in civilisation, but which a purer 

 and more natural life might restore to him. A civilised man 

 gets lost in the forest, and even in an unknown city. He 

 travels round and round in a circle, with a most uncomfortable 



