Sept. 5, 1884.] 



♦ KNOV/LEDGE ♦ 



189 



AN ILLUSTRATED 



MAGAZINE^SCIENCE 

 PuunlyWorded-Exactlydescribed 



LONDON: FRIDAY, SEPT. 5, 1884. 



Contents op No. 149. 



Our Two Brains. By Richard A. 

 Proctor 1S9 



Dreams. VIII. By Edward Clodd lOO 



The Westinghouse" Brake. By 

 "Trevitliicli" 193 



More About Sunflowers. By Grant 

 Allen I!I3 



The Earth'9 Shape and Motions : 

 IV. Determining the Shape of 

 the Earth (/Hi«.) By H. A. 

 Proctor 191 



An Address to the British Associa- 

 tion 19li 



The Electric Light in the Mecher- 

 nich Mines 197 



Optical Becreation. (Illun.) By 



F.R.A.S 19S 



Ttow American Carp are Destroyed. 



I {luui.) : im 



t other Worlds than Onrs. By M. 

 de Fontenelle. With Notes by 



Richard A. Proctor 200 



Muscular Contraction after Death 201 

 ] International Health Exhibition. 



XIII. ilUm.) 202 



I Editorial Gossip 203 



Reviews 2(H 



Miscellanea 205 



Correspondence 205 



, Oar Chess Column 208 



OUR TWO BRAINS. 



By Richard A. Proctor, 



THAT we have two brains may be said to be as certain 

 as that we have two eyes, two ears, and two nostrils. 

 Whether the two brains — I use the expression purposely, 

 instead of the usual expression, the two hemispheres of the 

 brain — act as independently of each other as the two eyes 

 or the two ears may be disputed. It may be maintained by 

 some that though they can thus act independently, should 

 occasion arise, the two halves of the brain, as a ru^e, work 

 not only as one but as parts of a single organ. Others may 

 hold (though the evidence is strong against this extreme 

 view) that one brain alone of the two can never suffice for 

 the process of reasoning. Others again may believe that 

 the two brains are absolutel}^ independent organs, a view 

 as extreme on the other side. But whatever opinion may 

 be held as to the action of the two brains, there can be no 

 question as to their existence in all normal case.''. That 

 the two brains are connected or associated together, is no 

 doubt true. So are the two eyes connected by the optic 

 commissure. But we do not speak of the two eyes as one 

 organ, though they serve a single sense. Even less can we 

 speak of the two brains as a single organ, when we find no 

 clear evidence even that they do the same work. If each 

 does or can do the same work, independently of the other, 

 they must be held to be distinct organs even as the right 

 eye is distinct from the left, when both work together in 

 ordinary vision. If the two brains do different work, they 

 are still more obviously distinct organs, — even as I, for 

 instance, more definitely recognise the duality of my eyes 

 than most persons, because, unlike most, I use one eye for 

 distant vision and the other for fine work at short focal 

 ranges. 



Of course a case might be made out for the oneness of 

 the brain as an organ, despite its duality of form, if it 

 could be shown that the individuality of the owner of the 

 brain depended wholly and solely on the co-existence, in a 

 complete state, of both hemispheres of the cerebrum (or of 

 both cerebra, as one should more correctly say). Even if 

 the two eyes, distinct though they are in appearance, were 



found to be severally essential to vision, we should be 

 obliged to regard them as a single organ, much as we 

 regard the upper arm and the lower arm as forming a 

 single limb. Nothing short of this, however, — and we 

 have no evidence even approaching this. — could compel us 

 to reject the doctrine of the duality of the brain. 



I propose to consider some of the evidence which 

 led Dr. A. L. Wigan to definitely enunciate this doctrine, 

 suspected apparently by Dr. Holland and others before 

 Wigau's time, but not clearly perceived or stated till he 

 wrote his work, now I believe out of print, " The Duality 

 of Mind." I would, however, at the outset, point out 

 how interesting, nay important, the inquiry is. How many 

 moral problems of difficulty find their solution if we recog- 

 nise in each one of us two minds, and in efiect two wills, 

 woi king it may be in harmony together at all times, or only 

 in h.rmony when the body is iu sound health, or one 

 usually holding sway over the other, or alternating in their 

 influence on conduct, or one it may be diseased and only 

 held in restraint by the other from guiding tlie man astray ! 

 Again, how many interesting mental problems appear in a 

 new light when thus viewed ! We have to consider two 

 memories, usually no doubt synchronising in their action, 

 but not necessarily working thus simultaneously ; two 

 attentions ; two reasoning processes ; and so forth. Again, 

 the two brains maj' differ in their physical powers, even as 

 one arm may be stronger than the other, one eye more sen- 

 sitive than the other to light, more easih' wearied, and so 

 on. Such cmsiderations are full of interest, and mav 

 throw important light on mental phenomena : but they are 

 most important in their bearing on character and conduct. 



I might here occupy much space with a description (in 

 outline) of the human brain as analysed and interpreted in 

 our time. But for my present purpose this is unnecessarv. 

 The following points, only, need here be specially noted :— 



If a vertical section be supposed to be taken through the 

 middle of the head from front to back, that is so as to 

 divide it (through the middle of the chin, nose, forehead, 

 crown, .and nape of the neck) into right and left portions, 

 this section will divide the whole nervous mass within the 

 skull into two symmetrical halves. Each part on one side 

 of the plane of division has its counterpart on the other 

 side, in the same way that each bone, muscle, tendon, fibre, 

 and nerve in the right arm has its counterpart in the left 

 arm. There is not perfect symmetry, nor exact corre- 

 spondence, any more than in the case of the two arms. 

 In some cases there is a marked want of symmetry, just 

 as in some men we see one arm much bttter developed than 

 the other : but such abnormal cases do not affect the 

 general truth that the right and left sides of the outer head 

 are symmetrical, and that the right and left arms corre- 

 spond to each other. 



Again, the principal parts of the cerebral mass, though 

 thus double, are connected across the median plane by 

 medullary bands called commissures, by which each part 

 on one side is united to its fellow on the other side. Thus 

 the great hemispheres (which in reality are not much more 

 than quarter spheres) are connected by the " great com- 

 missure " called the corpus callosiim ; the halves of the 

 cereheUuni (or little brain, occupying the lower and hinder 

 part of the cavity of the cranium) are connected by the 

 po)is Varolii or tii,ber annulare : and there are pther com- 

 missures ot smaller size. This connection of .tlie corre- 

 sponding parts of the two side brains no more cdiiljbines 

 them into a single brain than the two arms are' made one 

 by being attached to the same body. 



Between tie two so-called hemispheres of the brain there' 

 lies above a scythe-shaped extension of the membranoiife 

 covering called the di'.ra maUr; the point of the scythe is 



