PHYSIOLOGY OF SLEEP LEGENDRE. 599 



All these chemical theories of exhaustion or of intoxication arc cer- 

 tainly more important than those we previously considered. They 

 are in accord with the observation pure and simple that fatigue gen- 

 erally induces sleep and that sleep is a recuperator. They render 

 intelligible the alternating between wakefulness and sleep. They are 

 also the best-known theories and the ones generally adopted. Clapa- 

 rede, however, who has examined these theories, objects to them as 

 insufficient, and argues against them as follows: First, there is no 

 parallelism between exhaustion and sleep ; one can sleep without being 

 tired; great fatigue may disturb sleep. Second, according to the 

 chemical theories, the alternati@n of waking and sleeping might 

 assume a type of periodicity with short phases. Claparede says: 



Here is an individual who goes to sleep at midnight; at 10 minutes before midnight 

 he was — M. de la Palice can not dispute it — still wide awake. Why was he not asleep 

 at 10 minutes before midnight? Our physiologists say it was because the toxic waste 

 products had not then become sufficiently concentrated. But then why does not this 

 same individual awaken at 10 minutes or quarter past midnight since, if sleep stops 

 the accumulation of the toxic wastes without restricting their elimination, then rela- 

 tive proportion in the system would then return to what it was at 10 minutes before 

 midnight; that is, to a proportion favorable to awaking. 



Third, the toxic theory of sleep is antiphysiological, for it is sin- 

 gular that a process of intoxication severe enough to necessitate 

 eight hours of sleep should be repeated daily without at last causing 

 serious disorders. Finally, all the facts that have come under our 

 observation in regard to sleep — voluntary or involuntary drowsiness, 

 voluntary wakefulness, and the like — are not explainable by a chemi- 

 cal theory, no more than are other multiple forms of sleep, than the 

 physiological phenomena that accompany it, nor the dreams. An 

 observation of Vaschide and Vurpas on the Siamese twins shows well 

 the weakness of the chemical theories of sleep; in fact, these twins, 

 whose blood vessels communicate, often sleep or wake one after the 

 other and one could sleep while the other suffered from insomnia. 



In a general way, all physiological theories of sleep fail to success- 

 fully explain it, for none of them can take account of the psychological 

 phenomena which accompany it. We have seen that a person 

 sleeps or stays awake voluntarily or from habit, a condition that is 

 not within the province of the physiologist either to study or to 

 explain. 



Claparede, who has so well observed the impossibility of a physi- 

 ological solution, alone has sought to explain it by a theory both 

 psychological and physiological, which he has called the "biological" 

 theory of sleep. This biological theory is most interesting and ingen- 

 ious. It merits a place by itself and will hold our attention for a 

 time. According to Claparede, sleep is not merely a passive, negative 

 condition, a cessation of the organic functions. On the contrary, it 

 is itself a function, a positive activity, having its own biological 



