THEORIES OF SLEEP. 4:59 



to action, is simply occupied in the insensible repair of its 

 substance and is preparing itself for future work. The ex- 

 haustion of the muscles producas a sense of fatigue of the 

 muscular system, indisposition to muscular exertion, and a 

 desire for rest, not necessarily involving drowsiness ; fatigue 

 of the brain is manifested by indisposition to mental exer- 

 tion, dulncss of the special senses, and a desire for sleep. 

 Simple repose will relieve physiological fatigue of muscles ; 

 and, when a particular set of muscles has been used, the 

 fatigue disappears when these muscles alone are at rest, 

 though others be brought into action. Sleep, and sleep 

 alone, relieves fatigue of the brain. "Wlien the sleep has 

 continued long enough for the rest of the brain and the re- 

 pair of its tissue, we awake, prepared for new effort. 



AVe have now only to refer to a new theory of sleep, 

 proposed by Sommer. Taking as a basis the researches of 

 Pettenkofer and Yoit on respiration, Sommer advances the 

 idea that, when the brain is active, or while we are awake, 

 the system appropriates but a small quantity of oxygen in 

 respiration, and eliminates a relatively large proportion of 

 carbonic acid ; after a time, the oxygen thus appropriated is 

 consumed, and the system demands a new supply ; during 

 sleep, the organism appropriates oxygen largely, and elimi- 

 nates a relatively small amount of carbonic acid. When 

 the elimination of carbonic acid at the expense of the oxy- 

 gen stored up reaches a certain point, the necessity for a 

 farther supply of oxygen induces sleep ; and when, during 

 sleep, oxygen has been appropriated in sufficient quantity, 

 the system awakes, prepared for a new period of activity of 

 the animal functions. 1 



By reference to the researches of Pettenkofer and Yoit, 

 we find that these observers, in experiments on a man con- 

 fined in a chamber in which the interchanges of gases in 

 respiration could be estimated, noted, in twenty-four hours, 



1 SOMMER, Xeue Theorie des Schlafes.Zeitschrift fur rationeHe Median, 

 Dritte Reiho, Leipzig uiid Heidelberg, 1868, Bd. xxxiii., S. 214, et seq. 



