NVe 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 e.xcited 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 bmin, which I would call the centre qf 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 menta/ 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 this 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 bmin. 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 andi destruction may affect material thing,s. To I will, to feel, to perceive, to think, are so many states of Soul or acts of Mind.
Mind is, then, the mode of action of the Soul, as Life is the mode of action of the Body. The latter vve distinguish as material, and the phe nomena of life as specially belonging to orga nized matter; the former we denominate imma terial, to mark its essential difference from the body, admitting, however, that it exists in a mysterious union with the nervous system of the body in a manner so intimate that in a state of health the smallest change in either readily affects the other.
Such is the doctrine which seems most con sonant with reason and experience, and, above all, with revelation. But there are those who maintain that not only are certain states of mind preceded by certain states of body, but that all our ideas, our sensations, our volitions, are the result of, and as it were generated by, certain organic changes.