THE CEREBRUM, AND ITS FUNCTIONS. 819 



life of the Saviour ; towards that standard it is for the Christian disciple to 

 aspire. 1 



840. Of Sleep. It is a peculiar feature in the physiology of the Cerebral 

 and Sensorial 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 become in- 

 capacitated for further use. 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 felt or perceived ; 

 although an extraordinary impression, or even an habitual one upon which the 

 attention has been previously fixed as that at which the slumberer is to awake 

 himself ( 843), occasions a renewal of sensorial activity. 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 ac- 

 tivity 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 impressions which is observed after an over-dose of a narcotic, and 

 the intensification of ordinary sleep which is consequent upon extreme previous 

 fatigue. It is a matter of doubt, however, 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, we still dream, al- 

 though 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, as well as 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 ( 828). If this be the true account of the case, we may con- 

 sider that, in profound Sleep, the functional activity of the Cerebrum and of 

 the Sensory Ganglia is alike suspended ; that in Dreaming, the Cerebrum is 

 partially active, and that the Sensoriurn is in such a condition of recipience fcr 

 Cerebral impressions that the mind becomes directly conscious of them, whilst 

 it only becomes conscious of 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 current of ideas, and not by their power of exciting sensations, that we re- 

 cognize their operation under such circumstances. 



841. The state of Sleep is one to which there is beyond doubt a periodical 

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

 portion 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 Cere- 



' The careful study of the Epistles of St. Paul will show this to be the dominant idea of 

 this Apostle's teachings. Under the name of " the law," he refers to the spirit of bondage 

 or external coercion, which "was the schoolmaster to bring us to Christ;" whilst under the 

 designation of "the Gospel" he obviously desires to express that spirit of freedom or in- 

 ternal spontaneity which is the source of all that is truly noble in the Christian character. 



