MAURY ON SLEEP AND DREAMS. 377 



and that it can only be restored by food and sleep, 

 each severally needed for the process of repair. This 

 manner of viewing the nerve-power, or force, as an 

 element to be estimated by quantity by excess as 

 well as deficiency we believe to be not only just in 

 itself, but denoting a principle of singular value in 

 every part of physiology, and through physiology, in 

 pathology and the treatment of disease. Mr. Herbert 

 Spencer, in commenting on this subject with his 

 wonted ability, thus expresses the main facts, in which 

 all other writers on Sleep more or less concur : 



' Between this state (of sleep) and the waking state, the 

 essential distinction is a great reduction of waste. The rate 

 of waste falls so low, that the rate of repair exceeds it. It is 

 not that during the period of activity waste goes on without 

 repair, while during the period of inactivity repair goes on 

 without waste, for the two always go on together. Very pos- 

 sibly probably even repair is as rapid during the day as 

 during the night. But during the day the loss is greater 

 than the gain ; whereas during the night the gain is dimi- 

 nished hy scarcely any loss. Hence results accumulation. 

 There is a restoration of the nerve-tissue to its state of in- 

 tegrity.' 



Here, then, is a force, an agent, whether we call it 

 material or not, generated within the body, necessary 

 in its nature to all the functions of the body, but ex- 

 hausted in maintaining them, and requiring periods of 

 rest for its reproduction in adequate amount. When 

 calling sleep ' Nature's kind restorer,' we use a poetical 

 phrase, but express a physical fact. It is the restorer 

 of that which is expended and lost. Its intermittent 

 periods, its duration and degree, and even many of 



