104 HUMAN LONGEVITY. 



Look again at that which seems to make the greatest 

 breach in this unity of being, yet is itself an integral part 

 of life, and necessary to it the wonderful phenomenon of 

 Sleep. If called upon to name that part of our nature, which 

 is at once most marvellous in itself, and most prolific of con- 

 clusions beyond, we could not hesitate to find it in this great 

 function, so familiar to our experience, so obscure to our 

 philosophy. When Sir Thomas Brown describes sleep as ( the 

 brother of death, which extracteth a third part of our lives,' 

 he quaintly but strikingly denotes the wonderful fact of this 

 periodical intermission of ordinary life ; during which the 

 senses cease in great part to have relation to the world with- 

 out; and the mind, barely conscious of its own identity, 

 works in a vague succession of images and associations ; the 

 shadows sometimes of prior events, sometimes the seeming 

 creation of the very act of dreaming, and traceable to no 

 reality of waking existence. Scarcely can we abate our 

 wonder at this phenomenon of our nature, by placing what 

 we believe to be its true theory before us ; viz., that sleep is 

 not one, but an unceasing variety of states ; passing through 

 every stage and degree of change from perfect wakefulness 

 to the most complete suppression of all external conscious- 

 ness ; varying also at every moment in the degree in which 

 each particular sense and function of life is submitted to its 

 influence.* All these more special conditions of sleep do 

 rather enhance the wonder and the mystery of a state, which 

 thus occupies and engrosses a full fourth part of human ex- 

 istence on earth ; not less than a third, if we take infancy 

 and old age fairly into the calculation. The sleep and 

 various states of semi-consciousness produced by mesmeric 



* This view of Sleep as a succession of ever-changing conditions, I have 

 strongly urged in my volume on Mental Physiology, as the only one accordant 

 with truth, or capable of expounding the phenomena, mental and bodily, of 

 this mysterious function of life. 



