722v 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



neither pain nor disturbance of motion. Even 

 the electric current passed through them pro- 

 duces no sensible effect (Matteucci). We are 

 led, therefore, to the conclusion that these fibres 

 have endowments quite distinct from those of 

 sensitive and motor nerves, (a fact, by the 

 way, quite irreconcileable with the doctrine 

 which makes the brain the concourse of these 

 fibres,) and that they are internuncial between 

 parts which are beyond the immediate influence 

 of the ordinary physical agents, and which 

 have no direct connection with muscular organs. 

 The proper stimulant of these fibres is the 

 mind on the one hand, or the nutrient changes 

 in the brain on the other. But, under the 

 influence of a continued morbid irritation, they 

 may excite either pain or convulsion, or both, 

 as is frequently the case in disease of the 

 cerebral meninges ; this, however, is effected 

 through a change produced in the corpora 

 striata and optic thalami, and propagated thence 

 to the origins of motor and sensitive nerves, or 

 through irritation of the nerves of the meninges, 

 which affect the centres of motion and sensa- 

 tion, just as the nerves of other parts do. 



The experiments of Flourens and of Hertwig 

 show that removal of the cerebral hemispheres 

 produces a state of stupor, and, to use Flourens' 

 expression, as it were condemns the animal to 

 perpetual sleep, but deprives it even of the fa- 

 culty of dreaming. There is, however, no para- 

 lytic state produced by these mutilations. It is 

 evident, then, that the effect of these experi- 

 ments is psychical, and it may be adduced as 

 confirmatory of the view which associates the 

 functions of the cerebral convolutions with the 

 operations of the mind. 



Pathological anatomy affords interesting con- 

 firmation to this view. Inflammation of the 

 membranes of the brain, more especially of 

 the pia mater, is invariably attended by dis- 

 turbance of the mental faculties, as manifested 

 by more or less delirium. It appears that 

 any material alteration of the circulation in 

 the grey matter of the convolutions is capa- 

 ble of giving rise to delirium; in the in- 

 stance above quoted, the circulation in this 

 part is affected in consequence of the inflam- 

 mation 'of the pia mater, the bloodvessels of 

 the one being distinctly continuous with those 

 of the other ; but in other instances of violent 

 delirium, such, for example, as delirium tremens, 

 the vesicular matter of the convolutions is found 

 after death to be bloodless, as if its wonted 

 supply of blood had been cut off or abstracted 

 from it. We find this state in the delirium 

 after great operations, after puerperal floodings, 

 in the delirium of rheumatic fever, and in that 

 of gout, and likewise in that which occurs in 

 the more advanced stages of fever. 



We learn from the most trustworthy reports 

 of the dissections of the brains of lunatics that 

 there is invariably found more or less disease of 

 the vesicular surface and of the pia mater and 

 arachnoid in connection with it, denoted by 

 opacity and thickening of the latter with altered 

 colour or consistence of the former. 



From these premises it may be laid down as 

 a just conclusion that the convolutions of the 



brain, in other words, that vast sheet of vesicular 

 matter which crowns the convoluted surface of 

 the hemispheres, constitute the centre of intel- 

 lectual action, as distinguished from the centre 

 of volition and the centre of sensation (corpora 

 striata and optic thalami). It is essential to the 

 perfection of cerebral action that these centres 

 should be connected, and that the centre of in- 

 tellectual action should be capable of exciting 

 or of being excited by the centres of volition 

 and sensation. This connection and mutual 

 influence is effected through the innumerable 

 fibres which pass from the one to the other. 



To determine the precise connection which 

 exists between the mind and the brain is beyond 

 the reach of our means of observation and ex- 

 periment. All we are justified in affirming is 

 that the mental acts are associated with this por- 

 tion of the brain, which I would call the centre 

 of intellectual actions; and that the integrity 

 of this part is necessary to the perfect exer- 

 cise of the mind ; that, in the language of Cu- 

 vier, this centre is the sole receptacle in which 

 the various sensations may be as it were con- 

 summated, and where all sensations take a 

 distinct form and leave lasting traces of their 

 impression, serving as a seat to memory, a 

 property by means of which the animal is fur- 

 nished with materials for his judgment. 



The actions of the convoluted surface of the 

 brain, and of the fibres connected with it, belong 

 altogether to the class of mental nervous actions ; 

 that is, they either excite or are excited by 

 mental change. The physical changes in these 

 parts give rise to a corresponding manifestation 

 of ideas, and every thought is accompanied by 

 a change in (his centre. Modifications in its 

 nutrition, or interruptions to it, produce cor- 

 responding effects on the mind. An increased 

 activity of nutrient change causes a rapid de- 

 velopement of ideas, which, being generally un- 

 controllable by the will, and therefore undi- 

 rected, assumes the form of raving or delirium. 

 The shock of concussion so far checks the 

 organic changes of the vesicular surface, and 

 perhaps also of the fibrous matter, as to inter- 

 rupt for a time those conjoint actions of the 

 mind and the brain which are necessary for 

 perfect consciousness. The condensation of 

 the substance of the hemispheres, which is 

 produced by an apoplectic clot, or by the 

 effusion of some other foreign matter, prevents 

 a similar consent of action, and thus gives rise 

 to the phenomena of coma, a state in which all 

 mental nervous actions are destroyed or sus- 

 pended, and which, if continued long enough, 

 will annihilate the physical nervous actions 

 likewise. 



It will be observed that, in this description, 

 the workings of the mind are not viewed as 

 mere functions of the brain. The term Mind 

 expresses the mode of action of the Soul, an 

 entity which both reason and revelation assure 

 us is essentially different from the Body,* being 

 incorruptible and indestructible, in the sense 

 in which we suppose that both corruption and 

 destruction may affect material things. To 



* Ens incorpore ee prosapice, Prochaska. 



