PHYSIOLOGY OF THE NERVOUS SYSTEM. 



723B 



corresponding sensorial impression; and from 

 the connections which subsist between the reti- 

 nae, and still more from that between the cen- 

 tres of sensation,, these impressions become 

 fused into one. In like manner the organic 

 changes in the two brains developing nervous 

 force in similar modes and proportions, each 

 being capable of affecting the mind similarly, 

 although perhaps not identically, are yet so 

 united in their action that the double organic 

 affection acts on the mind as one. But if, 

 through default of the connecting media of the 

 two brains, or through lesion of one, the organic 

 changes in each do not harmonise with those 

 in its fellow, then it is plain that two separate 

 and distinct mental affections will result, and 

 more or less of confusion must ensue. I can 

 see no ground for inferring the existence of two 

 minds from such a supposition. The confu- 

 sion results from the want of simultaneous 

 affection of the same mind by two distinct and 

 separate brains. If, in vision, each centre of 

 sensation affected only its own mind, or, in 

 other words, developed only its own mental 

 phenomena, as Dr. Wigan's theory would 

 compel us to assume, then each mind would 

 perceive a different perspective projection 

 of the object presented to the eyes, and an 

 elaborate and complex mental process would 

 be required to combine the two sensorial im- 

 pressions. How much simpler is the view of 

 this process which assigns the combination of 

 the double impression to a physical union in 

 the brain of each physical change in the retina ; 

 so that, in truth, but one impression, different 

 from each of its excitant ones, reaches the 

 mind. So also, in the normal intellectual ac- 

 tion, the organic changes of the two brains are 

 united by the various transverse commissures, 

 so that but one physical stimulus affects the 

 mind and excites but one train of thought. 

 Not so, however, when from any defect in the 

 brains themselves, or in the commissures, the 

 physical conditions necessary for the organic 

 states of the two brains cannot be fulfilled. 



Dr. Wigan's theory is inconsistent with the 

 acknowledged fact of the existence of an im- 

 perfect symmetry of the convolutions in per- 

 sons possessing the highest order of mind. If 

 the two brains always act in harmony, there 

 ought to be perfect symmetry. But if we ad- 

 mit that the mind may have the initiative, then 

 it is easy to understand how one brain may be 

 used more than another. 



That a power exists of using one brain more 

 than another, seems probable from the more 

 frequent and more perfect use of one hand ; 

 and the existence of such a power implies also 

 a capability of keeping one brain in suspense 

 while the other is acting, under particular cir- 

 cumstances, just as we can suspend the use of 

 one arm or one finger or one eye, although the 

 exercise of its fellow prompts greatly to its 

 simultaneous action. 



Sleep is an affection of the centre of intel- 

 lectual action, a condition rendered necessary 

 by the incessant working of the mind. It is 

 indicated by the. cessation of all mental nervous 

 actions. In deep sleep the body is given up 



to the physical nervous actions only, without 

 which the functions of breathing, circulation, 

 &c., could not be carried on. Dreaming occurs 

 only in imperfect sleep, often, if not always, 

 just before waking, and serves to show how 

 the organic changes of the centre of intellectual 

 action, when uncontrolled, may produce the 

 most rapid trains of thought, recalling events 

 or impressions that have passed away, and 

 which we may have thought had been forgotten. 

 Coma is sleep of the profoundest kind, a 

 paralysis, indeed, of the centre of intellectual 

 action, as well as of sensation and volition. 

 It occurs under states of disease, which induce 

 compression of the brain, or under states of 

 shock, which suspend or greatly diminish its 

 natural changes, as in concussion. Or it may 

 be induced by the influence of certain poisons 

 of the sedative or narcotic kind, as opium and 

 belladonna, which, if given in too large a dose, 

 paralyse first the centres of mental nervous ac- 

 tions, and ultimately those of physical nervous 

 actions. 



Somnambulism must be regarded as a state of 

 intense dreaming, in which the person is 

 prompted to the performance of certain acts. 

 Talking in one's sleep, the curious changes of 

 position which are made under the influence of 

 nightmare, and even the most complex actions, 

 as walking, or taking things from one place to 

 another, or holding a long conversation, are all 

 induced by the same state, a morbid condition 

 of the centre of intellectual action, generally 

 produced by deranged assimilation or great pre- 

 vious disturbance of mind. The somnambulist, 

 in short, is one who dreams and acts in his 

 dream as if he were awake, and as if all the 

 phenomena of which he takes cognizance were 

 real. 



Delirium is a condition very analogous to 

 dreaming. The organic changes in the centre 

 of intellectual action are too rapid to be con- 

 trolled by the will, or the influence of the 

 centre of volition is impaired. The ravings of 

 a delirious patient generally take place uncon- 

 sciously, as if the centre of sensation were im- 

 paired likewise. In most instances, however, 

 the patient may be roused ; a strong stimulus, 

 as in addressing him with a loud voice, will 

 affect his centre of sensation, and he either 

 controls his thoughts for a brief space, and 

 directs his attention to what is going on, or the 

 effect of the stimulus is to direct his ravines 

 into some new channel. The incoherent and 

 unconnected manner in which thought follows 

 thought in the delirious stale is sufficient proof 

 that the centre of intellectual action requires 

 the controlling power of a will for perfect 

 trains of thought, as much as any particular 

 set of muscles requires the same influence for 

 the accomplishment of definite action. 



Delirium, indeed, may be viewed as a sub- 

 jective phenomenon of the centre of intellectual 

 action, just as tinnitus aurium or ocular spectra 

 are subjective phenomena of the centre of sen- 

 sation. 



In analysing the fibres. of the centrum ovale 

 we find that a large number of them is com- 

 missural, but that the greates proportion of 



