ix PSYCHO-PHYSICAL PHENOMENA 469 



insomnia. The new-born sleep more than adults, and old people 

 more than young. It is difficult to co-ordinate these facts with 

 the theory of a production of ponogenous. substances during the 

 activity of the waking state. 



If we conclude that the decline in the depth of sleep is in ratio 

 with the rate of elimination or destruction of the ponogenes, why 

 does sleep not attain its maximum profundity when the accumula- 

 tion of these substances is maximal, at the close of the long 

 waking period ? And why, after reaching its maximum after the 

 first or second hour, does sleep decrease sharply and afterwards 

 slowly to the moment of awakening, which is always preceded by 

 a second slight rise in the curve ? 



How, on the chemical theory, are we to account for the 

 hypnotising influence of darkness and silence, and, on the other 

 hand, of monotonous sounds ? How explain the fact that voluntary 

 effort or preoccupation with some idea may delay sleep for several 

 hours ; while, on the other hand, indifference to the surroundings, 

 passivity, or mere suggestion will suffice to induce sleep ? 



How does the chemical theory explain the phenomenon of pre- 

 arranged waking ? or that of partial sleep, during which the 

 attention is on guard, focussed on a single object ? How account 

 for the obstinate insomnia of neurasthenics and maniacal dements, 

 the profound sleep of some epileptics, the prolonged slumber of 

 certain invalids, the very light sleep of some hysterical patients ? 



But granting that these objections prove the inadequacy of 

 the chemical theory to account for all the phenomena of sleep, 

 it is undeniable that even if the action on the brain of the pono- 

 genous products developed during waking be not the determining 

 and inevitable condition of sleep, it nevertheless constitutes its 

 ordinary antecedent i.e. the predisposing cause. 



In order to complete the physiological account of sleep, it is 

 necessary to take into account not only its negative aspect, repre- 

 sented by the depression of the external senses, atonia of the 

 muscles, and suspension of the highest intellectual functions, but 

 also its positive aspect, that is its restorative property. Just as 

 the activity of waking predisposes to sleep, so the repose of sleep 

 prepares for awakening. 



It is important to note that the restorative efficacy of sleep is 

 something more than and different from the mere functional rest 

 of the organs of animal life, which may be obtained in the waking 

 state. The interruption of the sensorial and psychical current by 

 physiological sleep, if only for a few moments, will sometimes bring 

 a renovation and flow of vitality into the nervous system which 

 it is not possible to obtain while awake, even by lying down for 

 hours in darkness and silence. Evidently in sleep the anabolic or 

 assimilative processes prevail over the katabolic or dissimilative. 



Physiological sleep is quite different from the artificial narcosis 



