Feb. 20, 1S85.] 



♦ KNOWLEDGE ♦ 



111 



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'' MAGAZINE OF SCIENCE 

 PlainlyWorded-exactlyDescribed 



LOXDOX . fniDAY, FEB. l'O, 1885. 



COXTEXTS OF No. 173. 



Our Two Brains. Br Richard A. 



Proctor ■ IH 



On TermitM. {Vim.) By Siirgeon- 



Gt-nend R. F. Hutchinson 112 



PlcasjiDt Hours with the Microscope. 



(lltu-.\ Bt H. J. Slack 113 



A Remarkable Landslip atd its 



Causes. (///««.) IM 



The Origin of Comets. By Richard 



A. Proctor 113 



The Philosophy of Clothing. II. 



I //.'.<...) Bt W. Mattitu Willian s U7 

 Plant Life "and Planet Life. By 



Rihard A. Procter 118 



PAGB 



Future Arctic Woik. Bv Lient. 



OreolT .■ 119 



The Speedwell CyclinR Show 150 



Other Worlds than Ours 161 



The Younti Kleclrician. (Illwi.) 



By W. Slin-o 152 



Chapters on >Iodern Domestic Eco> 



nomr. XVI 151 



Editorial Gossip 153 



Highest Temperatures Endurable by 



Fish 158 



Correepondence 15ti 



Our Iiiv.-ntora' Column Idl 



Our (- .: - ' . ; I nil 11)2 



OUE TWO BRAINS. 



By Richap.d A. Proctor. 



(Continued from p. 102.) 



SUGGESTIONS FOR THE PKACTIGAL APPLICATION 

 OF TUE THEORY. 



IT has been shown that the fdculty of si)eech depends 

 either wholly or mainly on the left side of the brain. 

 A lesion in a particular region of this side produces the 

 loss of the faculty of expressiDg ideas by spoken words. 

 Out of more than a hundred cases of this peculiar disease 

 — aphasia — only one is known (and that case is doubtful) 

 in which the right side of the brain was diseased. This 

 seems to show that the two sides of the brain are distinct 

 one from the other. At first sight, however, the idea 

 might suggest itself that this evidence tended to prove that 

 the two portions of the brain discharge supplementary func- 

 tions. If the left side thus perform duties with which the 

 right side has nothing to do, presumably the right side may 

 perform duties from which the left side is free. This, 

 indeed, would appear to be the case ; but this is not a 

 necessary distinction; it may be regarded rather as the 

 result of habit, unconsciously exercised of course, since (as 

 yet, at any rate) we do not possess the power of deciding 

 that we will use this or that side of the brain. It appears 

 that usually the left brain is used in speech, as the i ight hand 

 is used in writing ; that a disease in the particular pait of the 

 left brain on which speech depends, causes aphasia, jae- 

 cisely as a disease of the right hand destroys the power of 

 writing (untU the left hand has been trained to the work) ; 

 and that by training both brains we should render this 

 particular form of cerebral disease less likely to cause loss 

 of speech, much in the same way that by training both 

 hands to write, we should dimiuish the chance of any such 

 cause as disease or accident depriving us of the power of 

 writing. 



Where the power of articulation is lost, it is not the 

 mere power of moving the muscles of the tongue, larynx 

 or chest, which is lost, but the memory of the mode of 

 directing the movements of those mussles. In many cases, 

 says Brown- Sequard, " a patient could move the tongue in 



any direction, could move the larynx, and utter rounds 

 very well ; but could not articulate, the nieiital part if tho 

 iiifchanical act being lost, not the mechanical action itself." 

 Sif;ht atlords evidence that tho distinct action of the two 

 sides of the brain is not incompatilile with the complete- 

 ness of the power possessed by either. WoUaston held ihafc 

 the right side of the base of the brain is the centre fir 

 sii,ht in the two light halves of the eye — that is, tiie half 

 of the right e) e towards the temple, and tlie half of the 

 left eye towards tl e nose ; while the left siJc of the Viase ot 

 the brain is the centre for sight in the two other halves — 

 the outer half of the left eye and the inner iulf of tin- 

 right eye. If this were so, the two halves of the bruin 

 would be, so far as sight is concerned, absolutely .supp'c- 

 mentary to each other, insomuch that a disease of eitlu r 

 half of the biain would render sight imperfect. It is not 

 altogether true, however, as Brown-Scquard states, that 

 only one-half of each object would be seen, for the whole of 

 an object may fall on either half of the utina. J!ut objects 

 looked at full front w(juld thus be divided, if the left side 

 of the brain were aflectcd, the left halves of the eyes would 

 act imperfectly — that is, the left halves of the visual field' 

 within the eje ; so that, in point of fact, oljects towards 

 the observer's right would be unseen, and i-iic rersa. 

 Wollaston himself was troubled occasionally liy a dcft-ct of 

 this kind. Tr} iug one day to read the name of an instru- 

 ment — the barometer — he could read only " meter, ' the 

 other part of the word, " Ijaro," being invisible. Agamix 

 was similarly affected. And many patients who are 

 afliicted with certain disorders of movement implyii g brain 

 disease have the same trouble — they see only half of objects 

 towards which the eyes are directly turned. Nor is tliis 

 the only evidence which at a first view seems to demi-i:- 

 strate Wollastou's theory. If the theory were true we 

 should expect to find that when only a small part of one 

 side of the brain — or, rather, of that region ou which sight 

 depends — was aflected, then only the half of one eye would 

 be de|jiived of sight. This has been found to be the case. 

 And, naturally, we should expect that if the other part of 

 the region (of the i-ame side of the brain) were aflected, 

 then the corresponding half of the other eye, and that 

 half only, would be deprived of sight. This also has 

 been found to be the case. Nevertheless, WoliastonV. 

 theory has to be abandoned bacau.se it does not account 

 for all the facts, and is opposed by three decisive facts 

 at least.* It has been shown in many instances that .v 

 disease in one half of the brain will produce complete loss 

 of sight (i.) of the two halves of the eye on the same side 

 as the diseased brain ; or (ii. ) of the two halves of the eye 

 on the opposite side; or (iii.) of the two halves of both 

 eyes. Manifestly, then, there is no necessary association 

 between either side of the brain and tho sight of either eye, 

 or of the two halves of either eye. Each side of the brain 

 possesses apparently the jiolnUial'Uy of rendering sight 

 perfect for both eyes. Admitting this, it is clearly a point 

 of great importance to inquire whether both sides of the 



* It is sinpuL-ir fiow soldoni the true rules which should guide iis 

 in selecting and rejecting tlienries arc recognised and miderfitood. 

 Over and over again we see it assumed, if not stated, that tliat 

 theory wliich accounts for tlic greatest number of facts is to be 

 adopted as the most probable. This is not by any means the case. 

 The true theory must, in re.ality, accord with all the facts, though 

 we may not be able to show that it does. Now, if a theory ac- 

 counts for several of the facts, and is not opposed hy a single 

 one, it has a much better claim to be adopted provisioually as tho 

 most probable, than another theory which accounts for a greater 

 nundjer of facts, or even for all the known facts save one, but \a 

 manifestly opposed by one fact. This is a rule of the utmost im- 

 portance in science, because often it enables us to select the true 

 theory, not by overpowering testimony of evidence in its favour, 

 but by consecutively rejecting all other possible theories. 



