OF SLEEP AND SOMNAMBULISM. 709 



v 



slumberer is to awake himself f 580), occasions a renewal of sensorial ac- 

 tivity. It is in this capability of being aroused by external impressions, 

 that the chief difference lies between Sleep and the abnormal condition of 

 Coma, whether this arise from the influence of pressure or effusion within 

 the cranium, or be consequent upon the poisoning of the blood by narcotic 

 substances, or follow a previous state of abnormal activity of the brain, 

 such as Delirium. Between these two conditions, however, every gradation 

 may be seen ; as in the gradually increasing torpor which results from slow 

 effusion within the cranium, the gradual loss of susceptibility to external im- 

 pressions which is observed on the application of Cold to the nervous cen- 

 tres, as in the interesting experiments of Dr. Richardson and Dr. Weir 

 Mitchell, 1 or after an overdose of a narcotic, as well as in the intensification 

 of ordinary sleep which is consequent upon extreme previous fatigue. But 

 it is a matter of doubt, whether the suspension of sensorial consciousness is 

 equally complete as regards internal or Cerebral changes; for some are of 

 opinion that, even in the most profound sleep, v/e still dream, although we 

 may not remember our dreams; whilst others (and among these the Author 

 would rank himself) consider that dreaming is a mark of imperfect sleep, 

 and that, in profound ordinary sleep, the Cerebrum in common with the 

 Sensory Ganglia, is in a state of complete functional inactivity. When 

 Dreaming takes place, there is usually a less complete exclusion of sensory 

 impressions, although-the perceptive consciousness may be entirely suspended : 

 so that the course of the dream may be influenced by them, although the 

 mind is not conscious of them as such ( 584). If this be the true account 

 of the case, we may consider that in profound Sleep the functional activity 

 of the Cerebrum and of the Sensory Ganglia is alike suspended ; but that in 

 Dreaming the Cerebrum is partially active, whilst the Sensorium is in such 

 a condition of receptivity for Cerebral (subjective) impressions that the mind 

 becomes directly conscious of them, though it only becomes conscious of (ob- 

 jective) impressions made upon the Organs of Sense, after their influence 

 has been transmitted through it to the Cerebrum, and has been, as it were, 

 reflected back by that organ. It is, in fact, by their influence upon the cur- 

 rent of ideas, and not by their power of exciting sensation*, that we recog- 

 nize their operations under such circumstances. 



573. The state of sleep is one to which there is beyond doubt a periodical 

 tendency ; for, when the waking activity has continued during a considerable 

 proportion of the twenty-four hours, a sense of fatigue is usually experienced, 

 which indicates that the brain requires repose; and it is only under some very 

 strong physical or moral stimulus, that the mental energy can be sustained 

 through the whole cycle. In fact, unless some decidedly abnormal condition 

 of the Cerebrum be induced by the protraction of its functional activity, Sleep 

 will at last supervene, from the absolute inability of the organ to sustain any 

 further demands upon its energy, even in the midst of opposing influences of 

 the most powerful nature. 2 That the strongest Volitional determination to 



1 See for Dr. Richardson's experiments, Medical Times and Gazette, 1867, vol. i, 

 p. 489 et seq. ; and for those of Dr. Mitchell, the American Journal of Medical 

 Science, 1867, p. 102. 



' Thus it is on record, that during the heat of the battle of the Nile, some of the 

 overfHtigued boys fell asleep upon the deck ; and during the last attack upon Rangoon, 

 the Captain of one of the war-steamers most actively engaged, worn out by the ex- 

 cess of continued mental tension, fell asleep, and remained perfectly unconscious for 

 two hours, within a yard of one of his largest guns, which was being worked energet- 

 ically during the whole period. So even the severest bodily pain yields before the 

 imperative demand occasioned by the continued exhaustion of the powers of the sen- 

 sorial centres; thus Damiens slept upon the rack, during the intervals of his cruel 

 sufferings ; the North American Indian at the stake of torture will go to sleep on the 



