708 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



6. Of Sleep and Somnambulism. 



572. It is a peculiar feature in the Physiology of the Cerebral and Sen- 

 sorial Ganglia, that their activity undergoes a periodical suspension, more 

 or less complete ; the necessity for this suspension arising out of the fact 

 that the exercise of their functions is in itself destructive to their substance, 

 so that, if this be not replaced by nutritive regeneration, they speedily be- 

 come incapacitated for further use. An ingenious theory of the cause of 

 sleep has been advanced by Sommer, 1 founded on the observations of Pet- 

 teukofer and Voit already alluded to ( 308, xi). Sommer observes that if, 

 as the experiments of Pettenkofer appear to show, oxygen is gradually being 

 stored up during sleep, a period will probably arrive when it exists in such 

 excess as materially to accelerate the metamorphosis of the nervous and 

 other tissues, and as a consequence awakening occurs. On the other hand, 

 during the waking state the stored up oxygen is gradually eliminated, as 

 shown by the large proportion of carbonic acid given off, until at length 

 when all the excess has been consumed, exhaustion and general relaxation 

 is experienced accompanied by the desire for sleep. This view has been ex- 

 pressed at considerable length by Pfliiger,' 2 who suggests that the waking state 

 is maintained by the violent oscillations almost comparable to small explo- 

 sions taking place in the molecules of the cerebral substance, owing to the 

 combination of the intramolecular oxygen with the carbon of the tissue. 

 These vibrations radiate outwards far and wide along the nerves in all direc- 

 tions. As the oxygen is gradually used up, the explosions become feebler, the 

 activity of all nervous processes less, mental operations are conducted with less 

 energy, the exhausted and quiescent nerves are no longer easily aroused by 

 impressions from without, and sleep results. On Dr. Cappie's 3 theory the links 

 in the causation of sleep are, first, that there is diminished molecular activity 

 of the cerebral cells, whilst coincideutly there is a change in the capillary 

 circulation of the brain, so that less blood is supplied to it, and it conse- 

 quently occupies less space. But as the brain-case must be constantly full, 

 the veins of the pia mater undergo gradual and proportional distension, 

 and although the absolute quantity of blood and the amount of internal 

 pressure remain unaltered, the direction of the pressure is modified. It 

 is less from within, and more on the surface of the organ, and with altered 

 direction of pressure the continued exercise of function is incompatible. 

 This view is quite in accordance with the interesting researches of Mr. 

 Arthur Durham 4 on the condition of the circulation in the Brain during 

 sleep, which have shown that the brain is then in an essentially bloodless 

 condition, and that not only the quantity but the rapidity of movement of 

 the blood in the vessels is'materially diminished ; and this is corroborated 

 by the observations of Dr. J. Hughlings Jackson on the ophthalmoscopic 

 condition of the Retina during sleep, 5 the optic disk being then whiter, the 

 arteries smaller, the veins somewhat larger, and the neighboring part of the 

 retina more aiuemic, than in the waking state. In ordinary profound Sleep 

 there is a "state of complete unconsciousness, so far as external phenomena 

 are concerned; no ordinary impressions upon the organs of sense being either 

 frit or perceived; although an extraordinary impression, or even an habitual 

 one upon which the attention has been previously fixed as that at which the 



1 Honleand Pfeu tier's Zeits. f. Rat. Med., lid. xxxii, 18G8, p. 214. 



* Pflii-er's Ardiiv, 1875, p. 4(18. 



:: Ciippic, The Causation of Sleep, 1872, p. 32. 



4 Guy'.- Hospital Report", Third Series, vol. vi. 



6 See Itoyul Loud. Ophth. Hosp. .Reports. 



