472 PHYSIOLOGY CHAP. 



Following on these lines, Claparede (1905) attempted to 

 formulate a biological theory of sleep, assigning to it the characters 

 of an instinct. We should not sleep if sleep were not in some 

 way beneficial to the organism. By means of daily sleep primitive 

 man avoided the manifold sufferings to which he would be 

 subject during the darkness of the night, and hereditary trans- 

 mission rooted an imperative need of it in the race. Claparede 

 holds sleep to be a positive function, and cites Cabanis, who wrote : 

 " Sleep is not a purely passive state : it is a peculiar function of 

 the brain which only occurs when a series of particular changes 

 occur in it. Cessation of these brings about awakening, or the 

 exterior causes of awaking produce it instantaneously." The same 

 thesis was taken up and developed on different lines by Sergueyeff, 

 Myers, Forel, and Vogt. 



According to Claparede, sleep and waking are defensive func- 

 tions, which come within the domain of biology, and are of great 

 importance in the struggle for existence both in animals and 

 man. " We sleep, not because we are poisoned or exhausted, but 

 to avoid falling into these states.' 3 All tendency to sleep dis- 

 appears in animals in the presence of danger, because a more 

 general instinct of defence intervenes for the protection of the 

 organism. 



Waking too according to Claparede is controlled by the 

 instinctive element of sleep. It is almost always provoked either 

 by an external or internal feeling, or by a dream. But it may 

 also be spontaneous when we no longer require sleep, "when 

 slumber ceases to be the most important instinct of the moment." 

 During sleep there is a not inconsiderable psychological activity, 

 although it is difficult to analyse this because it is largely sub- 

 conscious. In prearranged waking it is the voluntary resolution 

 previous to sleep that works occultly during slumber, and 

 causes the re-awaking. The cause of sleep is psychological; 

 it consists in " the reaction of indifference to the present situa- 

 tion." The restorative effect of sleep is due to rest, to the elimina- 

 tion of toxic products before their accumulation becomes injurious, 

 and to intensification of assimilative processes " the relaxation of 

 mental tension being probably compensated by an augmentation 

 of the vegetative tension." 



Claparede attempted to render a number of facts intelligible 

 by this theory of the genesis and nature of waking and sleeping, 

 but the transference of the problem from physiology to psychology 

 by no means solves it. His ingenious endeavour nevertheless 

 introduces us to the psychological phenomenology of sleep. 1 



VIII. From the psychological point of view sleep may 



1 The author is indebted to Professor G. Bilancioni for the exposition of the 

 facts and theory of sleep in the above paragraph, as also for that which follows on 

 dreams. 



