OFFICE OF SLEEP. 939 



ducing motion or action, that the object of ali- 

 ment is to supply materials for supporting respi- 

 ration, and for repairing the waste of the solids, 

 induced by exercise,- after which it is carried 

 out of the system by the different ernunctories, 

 in the form of carbonic acid, sweat, urine, &c. 



I shall now proceed to shew, that the proximate 

 cause of sleep is an expenditure of the substance and 

 vital energy of the brain, nerves, and voluntary 

 muscles, beyond what they receive when awake; 

 and that the specific office of sleep, is the resto- 

 ration of what has been wasted by exercise. 



That the necessity for sleep arises from an ex- 

 haustion of sensorial and muscular power, would 

 appear from the fact, that it is induced by intense 

 bodily pain, laborious exercise of the brain and 

 voluntary muscles ; when not carried so far as to 

 interrupt the nutritive process. So pressing is 

 the demand for it in cases of painful and difficult 

 parturition, that women often fall into a slumber 

 between the paroxysms of violent uterine con- 

 traction. They also require more sleep during 

 gestation, than at other times, owing to the ex- 

 penditure of blood and vitality in support of the 

 foetus. In accordance with these facts, sleep is 

 more profound and long continued, after the body 

 has been greatly wasted by protracted illness, or 

 exhausted by over exertion of any description, 

 whether of the nervous or muscular organs. 



Again : that the system actually increases in 



