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 298 w. MCDOUGALL : In the foregoing sketch of the series of changes consti- tuting the transition from the state of sleep to one of fully waking activity there is implied the view that the mainte- nance of the waking state depends upon the maintenance of a certain high degree of tonus throughout the neurones of the lower levels of the nervous system; and further it is implied that this in turn depends upon a constant liberation of energy or, as I prefer to call it, neurin, in considerable groups of afferent neurones, under the influence of peripheral stimuli. 1 This view is based on the characteristic differences of the states of sleeping and waking in the normal human being, and on the observed influence of stimuli to the peripheral nerves, and of the lack of such stimuli, in favouring the tran- sition from the one state to the other as traced above, and it receives confirmation from the consideration of such ab- normal cases as that reported by Strumpell. 2 In the case of this patient one eye and one ear remained the only sensitive organs, all other parts were anaesthetic, and whenever all stimuli were cut off from these two organs the patient always fell asleep in less than two or three minutes and could then only be wakened by flashing a bright light into his sound eye, or by repeatedly calling his name into his sound ear. It is further implied in the above account that we may re- gard all the neurones of the afferent side of the waking ner- vous system as constituting, in virtue of their interconnexions, a reservoir of energy, as containing a common stock of neurin upon which the various parts draw in turn as they become active, i.e. as they become in turn the principal paths of con- duction from afferent to efferent side. And it would seem that, while the maintenance of a certain degree of pressure or poten- tial is a necessary condition of the waking state, the degree of mental activity at any moment is more or less dependent upon and varies with the degree of this pressure, and there- fore dependent upon a continual peripheral stimulation of afferent neurones of the organs of sense and of organic sensi- bility. It would seem in fact, that, so far from sensory stimuli being detrimental to activity of the higher levels of the brain, all peripheral stimuli promote mental activity so long as they are not powerful enough to attract attention to themselves. That mental activity is favoured by the incidence of a large volume of sensory stimuli of a kind that does not powerfully 1 The over-excited brain which, in spite of fatigue and of the with- drawal of all but inconsiderable sensory stimuli, continues active and waking, is in an abnormal and semipathological condition, and is there- fore an exception to the rule and does not call for consideration here. 2 Deutsches Archiv f. klin. Mcdiziii, Bd. xxii.