466 PHYSIOLOGY CHAP. 



external stimuli, the dilatation of the cerebral vessels was, on the 

 contrary, preceded by a brief period of vascular contraction. 



Other authors have adduced diametrically opposite observa- 

 tions : during sleep they noted hyperaemia and cerebral vaso- 

 dilatation, instead of ischaemia and vaso-constriction. 



Czerny (1891) saw, in a boy who had a traumatic defect in 

 the skull, that when the patient closed his eyes and respiration 

 assumed the characteristic type for slumber, the height of the 

 cerebral pulsations increased, and attained its maximum in the 

 first half -hour of sleep, i.e. in the deepest phase. 



Brodmann (1902), by plethysmograph researches 011 a patient 

 trephined in the occipital region, stated that slumber was 

 characterised by a marked increase, awakening by a diminution, 

 in the volume of the brain. He contradicted the observations of 

 Howell and Lehmann and of Mosso, and demonstrated that 

 neither in sleeping nor waking was there any antagonism between 

 the cerebral circulation and that of the forearm. 



It is not easy to account for the contradictory character of 

 these results. For the theory of sleep it suffices to point out that 

 cerebral hyperaemia or anaemia are accessory phenomena, and not 

 the main factors on which sleep depends, since it supervenes 

 independently of the state of the cerebral circulation. Vulpian 

 observed that faradisation of the upper segments of the two cervical 

 sympathetic trunks does not produce general sleep, although it 

 induces a certain amount of cerebral ischaemia. On the other 

 hand, Brown-Sequard showed that bilateral section of the cervical 

 sympathetic, which is followed- by cerebral vaso- dilatation, does 

 not perceptibly disturb the rhythmic recurrence of sleep. 



Charles Bichet adduced several arguments in support of the 

 view that sleep is independent of changes in the cerebral circula- 

 tion. Sleep is almost universal in living beings ; the alterations 

 in the cerebral circulation in sleep or waking are not so great as 

 those due to simple variations in the position of the head ; even 

 decerebrated pigeons exhibit alternate periods of sleep and waking 

 after a few days, as did also the brainless dog of Goltz. 



Everything therefore speaks in favour of the view that the 

 depression of cerebral functions, which is the culminating 

 phenomenon of sleep, depends on a change of unknown character 

 in the nerve-elements of the brain, and that the changes in the 

 central circulation are only collateral secondary phenomena. 



One of the facts best ascertained and admitted by every one 

 is the beneficent and restorative action of sleep on the organism 

 as a whole, particularly on the psycho-physical functions of the 

 brain and nervous system in general. Hippocrates, Aristotle, 

 and Galen had already noted the deleterious effect of prolonged 

 waking. Bacon regarded sleep as an essential condition of the 

 prolonging of life. 



