380 FUNCTIONS OF THE NERVOUS SYSTEM. 



or is prevented, by the interruption of the usual channel of communication, 

 from operating on particular parts. Thus, in ordinary profound Sleep, which 

 is a state of complete unconsciousness, it is evident that the Cerebral Hemi- 

 spheres, and the Sensory Ganglia, are at rest; as the Cerebellum, also, may be 

 considered to be: but the Medulla Oblongata and Spinal Cord must be in com- 

 plete functional activity. The same is the case in profound Coma, resulting 

 from effusion of blood, or from narcotic poisons, but not affecting the power 

 of breathing or swallowing. It may be frequently observed, that the sleep is 

 not so profound as entirely to suspend the consciousness of the individual ; 

 and that various movements of an adaptive character are performed, tending 

 to relieve uneasiness resulting from various causes. In this condition it seems 

 not improbable, that the Sensory ganglia are in some degree awake, and that 

 the movements are of an instinctive nature; the mind of the individual not 

 being sufficiently active to discern the cause of the uneasiness, or to employ 

 his intelligence in the removal of it. Whenever Dreaming takes place, it is 

 evident that the Cerebrum is in a state of partial activity. The states of 

 Dreaming and Delirium, and many forms of Insanity, have considerable 

 analogy with each other; especially in the absence of the power which is so 

 characteristic of the well-regulated mind of Man, of controlling and regulating 

 the current of thought. One idea calls up another, according to their previous 

 associations; and the most incongruous combinations are frequently the result; 

 but it will generally, if not always, be found, that the ideas themselves have 

 been previously in the mind, and that no entirely new train of thought is 

 started. Of the degree in which, when the mind is thus closed to the external 

 \vorld, the hidden stores of Memory are opened to its search, many very 

 curious instances are recorded. 



500. The state of Somnambulism appears to be nearer to that of wakeful 

 activity of the whole mind, than is that of Dreaming. In the latter condition, 

 the individual is unconscious of external objects ; for, if they produce an effect 

 upon him, it is in modifying the current of ideas, frequently in some very 

 extraordinary manner : and he does not form any true perception or idea of 

 their nature. But in Somnambulism, his senses are partly awake, so that im- 

 pressions made upon them may be properly represented to the mind, and 

 excite there the ideas with which they are connected ; moreover the Cere- 

 bellum is also awake, so that the movements which the individual performs, 

 are perfectly adapted to their object; indeed, it has frequently occurred, that 

 the power of balancing the body has been so remarkably exercised in this 

 condition, that sleep-walkers have traversed narrow and difficult paths, over 

 which they could not have passed in open day, when conscious of their danger. 

 In Somnambulism, as in Dreaming, there is an evident want of voluntary 

 control over the thoughts ; their succession is more influenced, however, by 

 impressions received from without, than it is in dreaming; and hence the mind 

 . may sometimes be easily guided into a particular train, by properly directing 

 the impressions made upon the sensory organs. It may often be remarked, 

 however, that impressions which do not in some degree harmonize with the 

 train of ideas, are not received by the mind ; or, at any rate, they are not 

 applied to the correction of the erroneous notions which possess it. But there 

 are many different shades in the condition of the mind, between Dreaming 

 and Somnambulism ; the individual being, in some cases, much less conscious 

 of external objects, than he is in others. In some instances it appears as if 

 the mind was so wholly engrossed in a particular train of thought, that it could 

 not be affected by any new sensations, so that there is even an unconsciousness 

 of those which produce pain ; this has its parallel in the waking state. A 

 very remarkable characteristic of the state of Somnambulism, is the complete 

 isolation which commonly exists, between the trains of thought which then 



