723A 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



nature of the mind.* But no doubt his fears 

 are unfounded ; for if we hold that a connec- 

 tion subsists between soul and brain so intimate 

 that every change in either affects the other 

 more or less, surely the strongest inducement 

 is held out for the minutest investigation of 

 the organ which can exercise so wonderful an 

 influence on the immortal part of our nature. 



I would, then, lay it down that the proper 

 function of the brain is to generate the nervous 

 force, and that that force affects the soul and 

 excites its action for the developement of mental 

 phenomena. On the other hand, the action of 

 the soul affects the brain, exciting it to the de- 

 velopement of nervous force, and directing that 

 force for the production or regulation of other 

 corporeal phenomena. 



Taking this view of the nature of the mind, 

 and of the relation of mind and body, we may, 

 with advantage, arrange the principal mental 

 states into two classes, according as they are 

 preceded by certain states of body, or as they 

 precede and are capable of exciting certain 

 states of body. 



In the first class I would place sensation, 

 and such mental states as are immediately asso- 

 ciated with or produced by sensation, as the 

 emotions and the passions. To this class I 

 would likewise refer that peculiar power which 

 is, with the highest probability, exercised by 

 the cerebellum, and to which we must give the 

 name of balancing or coordinating power. It is 

 a power which, like the emotions and passions, 

 is exercised without any previous train of 

 thought or intellectual process, and seems sim- 

 ply to be evolved as an immediate consequence 

 of certain sensations, which are developed un- 

 der the influence of impressions made upon 

 the organs which are to be submitted to its 

 regulation. Thus, in locomotion, the exercise 

 of the muscles produces the sensation upon 

 which the evolution of this mental power de- 

 pends, which reacts upon the same muscles 

 with an intensity proportionate to the exciting 

 impulse. In the exercise of this power there is 

 much analogy with the ordinary reflex acts ; but 

 while the latter are purely physical in their 

 nature, the former may be clearly shown to be 

 mental. The proofs of this are derived, 1, from 

 its being never accomplished without conscious- 

 ness ; 2, from its being always associated with 

 volition ; 3, from the curious differences in the 

 mode of its exercise in different individuals, 

 according to differences of mental and physical 

 constitution, one man being expert and precise 

 in all his movements, another awkward and 

 clumsy; 4, from the marked improvement 

 which may be effected in it by instruction and 

 duly regulated practice. 



In the second class I would place volition 

 and attention. In these the mind has clear- 

 ly the initiative, and is capable of inducing 

 certain states of body, either to move certain 

 organs (voluntary motion), or to concentrate 

 one or more of the inlets of sensation upon 

 some external objects (attention). The power 



* Wigan on the Duality of die Mind. Lond., 

 1844. 



of abstraction, imagination, and all purely in- 

 tellectual processes, are obviously associated 

 with these. 



The symmetrical disposition of the parts of 

 the encephalon on each side of the median 

 plane has been recognised by all anatomists. 

 This symmetry is so complete that we may, 

 with perfect correctness, speak of two brains, 

 a right and a left brain, which are united to 

 each other by transverse commissures. The 

 ri^lst brain corresponds exactly with the left, 

 just as much as the right eye corresponds with 

 the left. This doubleness of the brain, no 

 doubt, accords curiously with the double- 

 ness of all the organs of sense, and very pro- 

 bably is rendered necessary by the existence of 

 the double set of inlets to sensation. It is 

 remarkable, however, that a perfect symmetry 

 of the convolutions is not found in the higher 

 races of mankind, and in individuals of high 

 intellectual powers ; and that the greater the 

 mental power, the less symmetrical are the 

 convolutions. In the inferior races, on the 

 other hand, as Tiedemann has well shown, the 

 symmetry of the convolutions is exact. 



Upon the proved existence of two brains, as 

 thus explained, Dr. Wigan, adopting the mate- 

 rialist view of mental phenomena, rests the 

 theory that the mind is dual ; that we have 

 two minds ; that each brain performs its own 

 mental functions, which are in perfect harmony, 

 if the two brains harmonise in quality, structure, 

 and action. 



It cannot be doubted that two brains, thus 

 symmetrical in structure, must have a tanta 

 mount symmetry of function, if I may be 

 allowed the expression ; and that, therefore, in 

 order to insure harmony of action between 

 them, and to prevent the actions of one from 

 interfering with or neutralising those of the 

 other, some such organic connection between 

 them is necessary as that which exists between 

 the two retinas, and which converts the sepa- 

 rate and in some degree dissimilar physical 

 impressions made on each of them into one 

 sensation. 



And as any interference with the organic 

 conditions necessary to secure single vision 

 with two eyes produces double vision, so it is 

 not unreasonable to expect that an analogous 

 imperfection in the organic union between the 

 two brains may occasion doubleness of mental 

 impression and" action. Such a conclusion, as 

 Dr. Wigan has ingeniously suggested, gives 

 the clue to the explanation of such phenomena 

 as states of double consciousness, delusions, 

 irregular volitions, and some forms of insanity ; 

 and, if fairly worked out by physiological psy- 

 chologists, may solve other obscurities con- 

 nected with the phenomena of the mind. 

 While, therefore, 1 admit that great practical 

 interest and value attach to Dr. Wigan's views 

 respecting the action of two brains, I am not 

 prepared to infer the existence of two minds 

 from that of two brains ; no more than I 

 can assume a duality of our visual sense 

 from the existence of two eyes. The two 

 cases, indeed, are strictly analogous. The 

 organic change in each retina developes a 



