PHYSIOLOGY OF SLEEP—LEGENDRE. 599 
All these chemical theories of exhaustion or of intoxication are 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- 
réde, 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 alternation of waking and sleeping might 
assume a type of periodicity with short phases. Claparéde 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, their 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. ; eye : 
Claparéde, who has so well observed the impossibility of a physi- 
ological solution, alone has sought to explain it by a = 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 Claparéde, 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 
