SLEEP. 



677 



SLEEP. This term is employed to desig- 

 nate that state of suspension of'the sensory and 

 motor functions, which appears to alternate, 

 in all animals, with the active condition of 

 those functions, and which may be made to 

 give place to it by the agency of appropriate 

 impressions upon the sensory nerves. 



Although this may seem a complex de- 

 finition of a state which seems to be in itself 

 so simple, yet it will not be found easy to 

 alter its character without rendering it less 

 stringent. We more especially desire to ex- 

 clude from it the abnormal condition of coma, 

 in all its forms ; whether resulting from the 

 influence of pressure or effusion within the 

 cranium, or consequent upon the poisoning of 

 the blood by narcotic substances, or occurring 

 as part of that inexplicable series of phenomena 

 which are termed hysterical. The state of 

 coma, where not so intense as to affect the 

 movements of respiration and deglutition, is 

 identical with profound sleep as regards its 

 obvious manifestations; but there is this im- 

 portant difference, that simple sleep may be 

 made to give place to activity by the ap- 

 plication of appropriate stimuli to the sen- 

 sorial system ; whilst in complete coma, no 

 impressions on the sensory nerves have any 

 power of bringing back the consciousness. 

 Between these two conditions, however, every 

 gradation may be seen ; as in the heavy sleep 

 produced by an over-dose of a narcotic, in in- 

 complete hysteric coma, or in the torpor 

 resulting from slow effusion within the cra- 

 nium. 



The necessity for sleep seems to arise from 

 the fact, that the exercise of the animal 

 functions is in itself destructive of the sub- 

 stance of the organs which minister to them ; 

 so that, if the waste or disintegration pro- 

 duced by their activity be not duly repaired, 

 they speedily become incapacitated for further 

 use. This doctrine is now so generally ad- 

 mitted, that it does not seem requisite to 

 adduce proofs in its support. The substance 

 of muscles is regenerated during the sus- 

 pension of their action in simple repose ; and 

 it is not essential that, for this purpose, a state 

 of unconsciousness should intervene. As 

 the substance of the nervous centres and 

 trunks, more especially the former, under- 

 goes a similar disintegration as a necessary 

 consequence of its activity, this too requires 

 a period of repose for its regeneration ; but 

 the repose, or suspension of functional acti- 

 vity, of the sensorial portion of the nervous 

 system, necessarily involves unconsciousness ; 

 and it appears to be on the nutritive regene- 

 ration which takes place during true sleep, 

 that its refreshing power depends. No such 

 refreshment is experienced from the uncon- 

 sciousness of coma, however prolonged ; and 

 there are some forms of ordinary slumber in 

 which it is more or less deficient. The or- 

 ganic functions are not affected in any con- 

 siderable degree by the suspension of the sen- 

 sorial ; for we find that not only are the 

 operations in which these functions essentially 

 consist uninterruptedly carried on, but that 



the muscles, nerves, and nervous centres also 

 which are concerned in maintaining them, are 

 enabled to sustain an unintermitted action. 

 Thus the movements of the heart are not, 

 in warm-blooded animals at least, normally 

 suspended, from the first development of that 

 organ until the close of life ; the respiratory 

 motions, in like manner, are kept up uninter- 

 ruptedly from birth to death ; and the pro- 

 pulsion of food along the alimentary canal 

 during sleep by the peristaltic contraction of 

 its muscular coat, the sustained action of the 

 sphincters, the peculiar position of the eyes, 

 and the active state of the extensor muscles 

 of the legs in animals which sleep standing, 

 are additional evidences that the state of con- 

 tinuous repose is not required for the reno- 

 vation of the powers of certain parts of the 

 nervous and muscular apparatus. To use Dr. 

 Marshall Hall's phraseology, " the true spinal 

 system never sleeps ;" and, whatever we may 

 think of the existence of his " true spinal " 

 system of nerve-fibres, as distinct from those 

 which minister to the functions of the ence- 

 phalon, there can be no longer any doubt that 

 the ganglionic portion of the spinal cord is a 

 distinct centre of nervous action, which re- 

 tains its power of actively responding to im- 

 pressions made upon it, during the profoundest 

 repose of the other centres ; whilst, from the 

 complete suspension of its functions, even for 

 a very brief period, death inevitably results. 



In following out our inquiry into the nature 

 of sleep, and of certain conditions allied to it, 

 we shall find it convenient to regard the 

 encephalon as composed of four leading or 

 primary divisions : 1. The medulla oblongata, 

 which essentially consists of a prolongation 

 of the spinal cord, including the centres of 

 respiration and deglutition ; and also having 

 incorporated with it, without properly form- 

 ing part of it, the ganglia of hearing and of 

 taste; 2. The ganglia of sensation, including, 

 with the olfactive, optic, auditory, and gus- 

 tative centres, the corpora striata and thalami 

 optici, which are probably, when taken to- 

 gether, to be regarded as the ganglia of tac- 

 tile sensation* : 3. The hemispheric ganglia 

 (ISolly), or peripheral portion of the cerebral 

 hemispheres: and 4. The cerebellum. 



The^yf? 1 *^ of these divisions really belongs to 

 the spinal cord, and, like it, is constantly 

 active. The second appears collectively to 

 form the true sensorinm, to which external 

 impressions must be conveyed, in order that 

 they may be felt (each class of sensations 

 being received through the medium of its 

 own ganglion), and from which proceeds the 

 stimulus to those automatic movements which 

 can only be excited by a sensation. Such 

 are the truly instinctive actions. The third 

 division, of which scarcely a rudiment exists 

 in the lowest fishes, although it constitutes by 

 far the largest proportion of the encephnlon 

 in man, seems to be the instrument through 

 which ideas are generated, by which they are 

 retained and made the subjects of intellectual 



* See British ami Foreign Medical Review, 

 vol. xxii. p. 510. 



x x 3 



