CHAPTER XCONFLICT OF THEORIES
It now remains to consider the source to which the preferential use of the right hand is to be ascribed. The dominant influence of the one cerebral hemisphere in relation to the discharge of nerve force to the opposite side of the body is a fact which is now familiar to the physiologist, and the influence of the left cerebral hemisphere on the action of the right hand has already been alluded to. But this extremely probable source of right-handedness long eluded inquirers, as will be seen from arésuméof the various hypotheses suggested by eminent anatomists and physiologists. A very slight consideration of the evidence already adduced in proof of the same prevalent usage from earliest times precludes the idea of its origin in any mere prescribed custom,enforced and developed by education into a nearly universal habit. This becomes the more manifest when it is traced back to primæval races; found incorporated in ancient and modern, savage and civilised languages, and uncontroverted by any evidence calculated to discredit the indications that it was a characteristic of palæolithic and neolithic man.
The inevitable conclusion forced on the inquirer is that the bias in which this predominant law of dexterity originates must be traceable to some specialty of organic structure. On this assumption one feature in the anatomical arrangement of the most important vital organs of the body presents such a diversity in their disposition as would seem to offer a sufficient cause for greater energy in the limbs on one side than on the other, if accompanied by exceptional deviations from the normal condition corresponding to the occurrence of left-handedness; and in this direction a solution has accordingly been sought. The bilateral symmetry of structure, so general in animal life, seems at first sight opposed to any inequality of action in symmetrical organs. But anatomical research reveals the deviation of internal organic structure from such seeminglybalanced symmetry. Moreover, right or left-handedness is not limited to the hand, but partially affects the lower limbs, as may be seen in football, skating, in the training of the opera-dancer, etc.; and eminent anatomists and physiologists have affirmed the existence of a greater development throughout the whole right side of the body. Sir Charles Bell says: “The left side is not only the weaker, in regard to muscular strength, but also in its vital or constitutional properties. The development of the organs of action and motion is greatest upon the right side, as may at any time be ascertained by measurement, or the testimony of the tailor or shoe-maker.” He adds, indeed, “Certainly this superiority may be said to result from the more frequent exertion of the right hand; but the peculiarity extends to the constitution also, and disease attacks the left extremities more frequently than the right.”
With the left-handed, the general vigour and immunity from disease appear to be transferred to that side; and this has naturally suggested the theory of a transposition of the viscera, and the consequent increase of circulation thereby transferred from the one side to the other. But the relative position of the heart is so easily determined in theliving subject, that it is surprising how much force has been attached to this untenable theory by eminent anatomists and physiologists. Another and more generally favoured idea traces to the reverse development of the great arteries of the upper limbs a greater flow of blood to the left side; while a third ascribes the greater muscular vigour directly to the supply of nervous force dependent on the early development of the brain on one side or the other.
So far as either line of argument prevails, it inevitably leads to the result that the preference of the right hand is no mere perpetuation of convenient usage, matured into an acquired, or possibly an hereditary habit; but that it is, from the first, traceable to innate physical causes. This, as Sir Charles Bell conceives, receives confirmation from the fact already referred to, that right or left-handedness is not restricted to the hand, but affects the corresponding lower limb, and, as he believes, the whole side; and so he concludes thus: “On the whole, the preference of the right hand is not the effect of habit, but is a natural provision; and is bestowed for a very obvious purpose.” Nevertheless, the argument of Sir Charles Bell is, as a whole,vague, and scarcely consistent. He speaks indeed of right-handedness as “a natural endowment of the body,” and his reasoning is based on this assumption. But much of it would be equally explicable as the result of adaptations following on an acquired habit. Its full force will come under consideration at a later stage. Meanwhile it is desirable to review the various and conflicting opinions advanced by other inquirers.
The theory of Dr. Barclay, the celebrated anatomist, is thus set forth by Dr. Buchanan, from notes taken by him when a student: “The veins of the left side of the trunk and of the left inferior extremity cross the aorta to arrive at the vena cava; and some obstruction to the flow of blood must be produced by the pulsation of that artery.” To this Dr. Barclay traced indirectly the preferential use of the right side of the body, and especially of the right hand and foot “All motions,” he stated, “produce obstruction of the circulation; and obstruction from this cause must be more frequently produced in the right side than the left, owing to its being more frequently used. But the venous circulation on the left side is retarded by the pulsation of the aorta, and therefore the more frequentmotions of the right side were intended to render the circulation of the two sides uniform.” The idea, if correctly reported, is a curious one, as it traces right-handedness to the excess of a compensating force for an assumed inferior circulation pertaining naturally to the right side; and incidentally takes into consideration an abnormal modification affecting the development or relative disposition of organs. Both points have been the subject of more extended consideration by subsequent observers. It is curious, indeed, to notice how physiologists and anatomists have shifted their ground, from time to time, in their attempts at a solution of what has been very summarily dismissed by others as a very simple problem; until, as Dr. Struthers remarks, it “has ceased to attract the notice of physiologists only because it has baffled satisfactory explanation.”
The eminent anatomist, Professor Gratiolet, turned from the organs in immediate contact with the arm and hand, and sought for the source of right-handedness in another and truer direction, though he failed to realise its full bearings. According to the Professor, in the early stages of fœtal development the anterior and middle lobes of thebrain on the left side are in a more advanced condition than those on the right side, the balance being maintained by an opposite condition of the posterior lobes. Hence, in consequence of the well-known decussation of the nerve roots, the right side of the body,—so far as it is influenced by brain-force,—will, in early fœtal life, be better supplied with nervous force than the left side; and thereby movements of the right arm would precede and be more perfect than those of the left. The bearings of this line of argument in its full compass will come more fitly under review at a later stage.
Dr. Andrew Buchanan, Professor of Physiology in the University of Glasgow, in a paper communicated by him to the Philosophical Society of Glasgow in 1862, entitled “Mechanical Theory of the predominance of the right hand over the left; or more generally, of the limbs of the right side over those of the left side of the body,” aimed at a solution of the question in a new way. According to him, “the preferential use of the right hand is not a congenital but an acquired attribute of man. It does not exist in the earliest periods of life.” Nevertheless, “no training couldever render the left hand of ordinary men equal in strength to the right;” for “it depends upon mechanical laws arising out of the structure of the human body.” This theory is thus explained: In infancy and early childhood there is no difference in power between the two sides of the body; but so soon as the child becomes capable of bringing the whole muscular force of the body into play, “he becomes conscious of the superior power of his right side, a power not primarily due to any superior force or development of the muscles of that side, but to a purely mechanical cause. He cannot put forth the full strength of his body without first making a deep inspiration; and by making a deep inspiration, and maintaining afterwards the chest in an expanded state, which is essential to the continuance of his muscular effort, he so alters the mechanical relations of the two sides of his body that the muscles of his right side act with a superior efficacy; and, to render the inequality still greater, the muscles of the left side act with a mechanical disadvantage.” Hence the preference for the right side whenever unusual muscular power is required; and with the greater exercise of the muscles of the right side theirconsequent development follows, until the full predominance of the right side is the result.
This theory is based not merely on the preponderance of the liver and lungs on the right side, but on these further facts: that the right lung is more capacious than the left, having three lobes, while the left has only two; that the liver, the heaviest organ of the body, is on the same side; and that the common centre of gravity of the body shifts, more or less, towards the right, according to the greater or less inspiration of the lungs, and the consequent inclination of the liver resulting from the greater expansion of the right side of the chest. Herein may possibly lie one predisposing cause leading to a preferential use of the right side. But the evidence adduced fails to account for what, on such a theory, become normal deviations from the natural action of the body. The position of the liver and the influence of a full inspiration combine, according to Dr. Buchanan, to bring the centre of gravity of the body nearly over the right foot. Hence in actively overcoming a resistance from above, as when the carter bears up the shaft of his cart on his shoulder, the muscular action originates mainly with the lowerlimb of the same side, which partakes of the same muscular power and development as the corresponding upper limb. On all such occasions, where the muscular action is brought directly into play in overcoming the weight or resistance, Dr. Buchanan affirms that the right shoulder is much more powerful than the left, but in the passive bearing of weights it is otherwise. The very fact that the centre of gravity lies on the right side gives a mechanical advantage in the use of the left side in sustaining and carrying burdens; and this assigned pre-eminence of the left side and shoulder, as the bearer of burdens, is accordingly illustrated by means of an engraving, representing “a burden borne on the left shoulder as the summit of the mechanical axis passing along the right lower limb.”
In the year following the publication of Dr. Buchanan’sMechanical Theory, Dr. John Struthers, Professor of Anatomy in the University of Aberdeen, communicated to the EdinburghMedical Journala paper, “On the relative weight of the viscera on the two sides of the body, and on the consequent position of the centre of gravity to the right side.” In this he shows that the viscera situated on theright side of the medial line are on an average 22·75 oz. av. heavier than those on the left side. The right lung, in the male, weighs 24 oz., the left 21, giving a preponderance of 3 oz. in favour of the right. The average weight of the heart, in the male, is 11 oz. But the left side is not only the larger, but the thicker, and as the result of careful experiments by Dr. Struthers, he assigns to the right side a full third of the weight of the heart, or 3¹⁄₂ oz. for the right, and 7¹⁄₂ for the left side. Other viscera are estimated in like manner, with the result from the whole that the centre of gravity of the body, so far as it depends on their weight and position, is nearly three-tenths of an inch distant from the medial plane towards the right side. As a physical agent constantly in operation in the erect posture, Dr. Struthers states that this cannot but exert an influence on the attitudes and movements of the body and limbs; and he accordingly indicates his belief that this deviation of the centre of gravity furnishes the most probable solution of the causes “of the preference of the right hand by all nations of mankind.”
The value of Dr. Struthers’s determination of the exact weight and relative eccentricity of theviscera on the two sides of the body was fully recognised by Dr. Buchanan; and in a communication to the Philosophical Society of Glasgow in 1877 he stated that he had been led to greatly modify his earlier opinions. He had, as shown above, ascribed the predominance of the right hand over the left to the mechanical advantage which the right side has in consequence of the centre of gravity inclining to it. But he says in his later treatise, “I judged hastily when I inferred that this is the ground of preference which prompts the great majority of mankind to use their right limbs rather than their left. The position of the centre of gravity on the right side is common to all men of normal conformation, and furnishes to all of them alike an adequate motive, when they are about to put forth their full strength in the performance of certain actions, to use the limbs of the right side in preference to those of the left. But such actions are of comparatively rare occurrence, and the theory fails to explain why the right limbs, and more especially the right hand, are preferred on so many occasions where no great muscular effort is required; and fails still more signally to explain why some men give a preferenceto the limbs of the left side, and others manifest no predilection for either.” Dr. Buchanan accordingly proceeds to show that there is not only the element of the position of the centre of gravity as the pivot on which all the mechanical relations of the two sides of the body turn; but there is, as he conceives, this other and no less important element. “The centre of gravity situated on the right side is variously placed upwards or downwards, according to the original make or framework of the body.” In the great majority of cases this lies above the transverse axis of the body, with a consequent facility for balancing best, and turning most easily and securely on the left foot, with the impulsive power effected by the muscles of the right lower limb. Man is thus, as a rule, right-footed; and, according to Dr. Buchanan, by a necessary consequence becomes right-handed. By a series of diagrams he accordingly shows the assumed variations: (1) the centre of gravity above the transverse axis, with its accompanying right-handedness; (2) the centre of gravity corresponding with the transverse axis, which he assigns to the ambidextrous; and (3) the centre of gravity below the transverse axis begetting left-handedness. Thewhole phenomena are thus ascribed to the instinctive sense of equilibrium, which constitutes a nearly infallible guide in all the movements of the human body. The greater development of the organs of motion of the right side is therefore, as he conceives, not congenital, but arises solely from the greater use that is made of them. The relative position of the centre of gravity depends accordingly on the original conformation of the body. Broad shoulders, muscular arms, a large head and a long neck, all tend to elevate the centre point; while the contrary result follows from width at the haunches and a great development of the lower limbs.
The intermediate condition, in which the centre of gravity falls upon the transverse axis, with no instinctive tendency to call into action the muscles of the one side of the body in preference to those of the other, constitutes, according to Dr. Buchanan, the most happy conformation of the body. “It belongs,” he says, “more especially to the female sex. It is this that so often renders a young girl a perfect model of grace and agility. It is the same conformation that enables the ballet-dancer to whirl round on her one foot till the spectators aregiddy with looking at her, when she completes her triumph by revolving with the same ease and grace on her other foot also.” He further adds: “If accurate statistics could be obtained, I believe it would be found that while a very great majority of males are right-handed, the proportion of females is less; and that, on the contrary, a larger proportion of females than of males are ambidextrous or left-handed.”
Consistently with the ideas thus set forth, both Dr. Buchanan and Dr. Struthers regard right-handedness as an acquired habit, though under the influence and control of the mechanical forces indicated by them. “As the question,” says the latter, “in so far as it can bear on the cause of the preference of the right hand, must turn on the weight and position of the viscera in the child at the period when the predominance of the right hand is being gradually developed, in the second and third years, and afterwards, it is necessary to make the calculation from the facts as presented in children.” In a letter to myself he thus writes: “I have again and again verified the fact in my own children, that in early childhood there is no preference for one hand more than the other.”But this, as has been already shown, may be partly due to modes of nursing and other temporary causes affecting the child in its first infantile stage; and though it may undoubtedly be affirmed of many, if not indeed of the majority, of children at that stage: a certain number will be found to manifest a distinct preference, at a very early age, for one or the other hand. In the case of a niece of my own, the left-handedness showed itself very soon; and in my grandson it was independently observed by his mother and nurse, and brought under my notice, that so soon as he was able to grasp an object and transfer it from one hand to the other, he gave the preference to the left hand. A like decided preference for the right hand, though doubtless also comparatively rare, is more frequent; and the farther research is carried, the more manifest does it appear that—whatever be the originating cause,—the preferential use of what we designate the right hand is instinctive with a sufficiently large number to determine the prevalent usage; while with a smaller number an equally strong impulse is felt prompting to the use of the left hand, in defiance of all restraining influences. It is indeed always necessary to give full weight to the influencesof education, the whole tendency of which, from early childhood, operates in one direction. The extent to which this is systematically employed to develop the use of the one hand at the expense of the other, is illustrated by the conventional rules for the use of the knife and fork. It is not sufficient that the knife shall be invariably held in the right hand. The child is taught to hold his knife in the right hand and his fork in the left when cutting his food; but when either the fork or spoon is used alone, it must forthwith be transferred to the right hand. All voluntary employment of the left hand in any independent action is discountenanced as awkwardness or gaucherie; and thus, with a large majority, especially among the more refined and conventional classes of society, it is rendered a comparatively useless member, employed at best merely to supplement the other.
Reference has already been made to more or less definite allusions to an exceptional prevalence of left-handedness in the Punjab, and among the Sandwich Islanders, the Hottentots, and South African Bushmen; but they rest apparently on very partial and limited observations. So far as appears, it may be confidently assumed that left-handednessis little more prevalent among the rude and uncultured classes of society, or among savage than civilised races; as would certainly be the case if right-handedness mainly depended on an acquired habit. The Rev. George Brown, who has spent upwards of fourteen years as a missionary among the Polynesians, informs me that left-handedness is as rare among the natives of the Pacific Islands as with ourselves; while in all their languages the distinction is clearly indicated. Dr. Rae, whose own inveterate left-handedness was calculated to draw his attention to its manifestation among the Indians and Eskimos with whom he was brought into prolonged contact, only noticed such an amount of ambidextrous facility as is naturally developed in the paddler, the trapper, and lumberer, in the exigencies of forest and hunter life. A similar opinion was expressed to me by Paul Kane, whose wanderings as an artist among the tribes of British North America gave him exceptional facilities for observation; and this conclusion accords with the experience of members of the Canadian Geological Survey.
Turning next to the idea set forth by Dr. Buchanan as to the greater preponderance of ambidexterity or left-handedness among females, theresults of my own observation by no means tend to confirm this. I have already noted the case of a lady whose left-handedness is accompanied by great dexterity. I have repeatedly met with cases of ladies who use the needle skilfully with the left hand; but the results of inquiries addressed to musicians and music teachers indicate that in the great majority of cases the cultivation of the left, as the weaker or less skilful hand, has to be sedulously enforced in the training of the female organist and pianist. It is because left-handed pianists are rare that their exceptional dexterity is noted, as in the case of a Canadian lady referred to above: “She had great advantages from her left-handedness. She was a very good performer on the piano, and her bass was magnificent.”
Again as to the pirouetting of the trained ballet-dancer, I have been assured that much practice is required to obtain equal facility on either foot. Dr. Buchanan traces the development of the limbs in their active use from the first effort of the child to stand erect; next, the learning to balance itself and turn round on a single foot, and so through a succession of stages, until at length “the child becomes right-footed. It is not till long after thatthe right arm acquires its predominance.” But the co-ordination of the right or left hand and the corresponding foot is by no means so invariable as to justify any such theory. Hopping, pirouetting, and standing on one foot are comparatively exceptional actions. The two lower limbs are most frequently employed in necessarily alternate locomotion. The use of the lower limbs, moreover, is much more independent of direct conscious volition than that of the hands, and the purposes to which their action is applied are rarely of a nature to invite special attention to them. There is, however, an instinctive tendency with many, if not indeed with the majority, to use one foot in preference to the other, but not necessarily the corresponding one to the dexterous hand, be it right or left. In skating, for example, where military training has not habituated to the use of the left foot in starting, most persons have an instinctive preference for one foot. So also in football, it is not with most players a matter of mere chance which foot will be used in starting the ball. Possibly the same reason may help to account for the invariable tendency of a blindfold walker to deviate to one side or the other. It is scarcely possible to walk in a straight linewith the eyes shut. The one leg apparently tends to outwalk the other. Guided mainly by my own experience, I remarked, when first writing on this subject, that “the same influences appear to affect the whole left side, as shown in hopping, skating, football,” etc. But this is partial and uncertain. Dr. Brown-Sequard affirms that right-sidedness affects the arms much more than the legs, and in proof of this he states that “it is exceedingly rare that the leg is affected in the same degree by paralysis as the arm.” Dr. Joseph Workman, for many years Medical Superintendent of the Provincial Lunatic Asylum at Toronto, thus writes to me: “When you say that left-footedness is (only) as frequent as left-handedness, I am quite sure you are in error. I remember well, when I was a boy, observing the fact among labouring men engaged in what was called in Ireland ‘sodding’ potatoes, in ridges about five feet wide, instead of planting in drills, that in any given number of men, from four up to a dozen, right and left-footedness prevailed about equally. Each pair carrying up the work of a ridge required to be right and left-footed men. I am myself left-footed; and of eight brothers, I believe about four were left and four right-footed.Sir Charles Bell, in asserting that ‘no boy, unless he is left-handed, hops on the left foot,’ asserts far more than the fact. I believe every boy will hop on hisspade foot; at least I do so, and I am not left-handed; and I instinctively do so because I dig with this foot.”
Dr. Buchanan states that “in all adults who use the right hand in preference to the left—that is, in the great majority of mankind,—the muscles of the right side, as well as the bones and other organs of motion, are more highly developed than those on the left side;” and the predominance of the upper limb follows, as a rule, the previous development of the lower limb on the same side. The power of overcoming weight or resistance, and that of passively bearing weights, he assigns to opposite sides,—both naturally resulting from the centre of gravity lying on the right side. If such be the case, the great majority of mankind should instinctively use the same side in bearing a burden. A favourable opportunity occurred for testing this question. During a voyage of some days in one of the large steamboats on the Mississippi River, my attention was attracted by the deck-porters, who at every landing are employed in transporting the freight toand from the levee, and in supplying the vessel with cordwood. They constitute, as a class, the rudest representatives of unskilled labour, including both whites and negroes. For hours together they are to be seen going at a run to and from the lower deck of the vessel, carrying sacks of grain, bales, chests, or bundles of cordwood. Watching them closely, I observed that some gave the preference to the right and some to the left shoulder in bearing their burden; and this whether, as with bale and sack, they had it placed on their shoulders by others, or, as with cordwood, they took the load up themselves. Noting in separate columns the use of the right and left shoulder, and in the case of loading with cordwood the employment of the right and left hand, I found the difference did not amount to much more than 60 per cent. In one case I noted 137 carry the burden on the left shoulder to 81 on the right; in another case 76 to 45; and in the case of loading cordwood, where the natural action of the right hand is to place the burden on the left shoulder, so that the use of the right shoulder necessarily implies that of the left hand, the numbers were 65 using the left shoulder and 36 the right. Here, therefore, a practical test of a verysimple yet reliable kind fails to confirm the idea of any such mechanical cause inherent in the constitution of the human frame, tending to a uniform exertion of the right side and the passive employment of the left in muscular action.
While thus questioning some of the assumptions and deductions set forth by Dr. Buchanan, it must be acknowledged that his later theory has this great advantage over other attempts to account for right-handedness, that it equally meets the cases of deviation from prevalent usage. No theory is worthy of serious consideration which deals with left-handedness as an exceptional deviation from habitual action; as where, in his earlier treatise, Dr. Buchanan expressed the belief that many instances of left-handedness are “merely cases of ambidextrousness, when the habit of using the left side, in whatever way begun, has given to the muscles of that side such a degree of development as enables them to compete with the muscles of the right side, in spite of the mechanical disadvantages under which they labour.” “There is an awkwardness,” he added, “in the muscular efforts of such men which seems to indicate a struggle against nature.” But for those indisputable cases of “men who unquestionably usetheir left limbs with all the facility and efficiency with which other men use their right,” he felt compelled either to resort to the gratuitous assumption of “malformations and pathological lesions in early life, diseases of the right lung, contraction of the chest from pleurisy, enlargement of the spleen, distortions of the spine,” etc.; or to assume a complete reversal of the whole internal organic structure.
More recently, Dr. Humphry of Cambridge has discussed the cause of the preferential use of the right hand in his monograph onThe Human Foot and Human Hand, but with no very definite results. Many attempts, he says, have been made to answer the question, Why is man usually right-handed? “but it has never been done quite satisfactorily; and I do not think that a clear and distinct explanation of the fact can be given. There is no anatomical reason for it with which we are acquainted. The only peculiarity that we can discern is a slight difference in the disposition, within the chest, between the blood-vessels which supply the right and left arms. This, however, is quite insufficient to account for the disparity between the two limbs. Moreover, the same disposition is observed in left-handed persons and in some of the lower animals;and in none of the latter is there that difference between the two limbs which is so general among men.” Dr. Humphry accordingly inclines to the view that the superiority of the right hand is not natural, but acquired. “All men,” he says, “are not right-handed; some are left-handed; some are ambidextrous; and in all persons, I believe, the left hand may be trained to as great expertness and strength as the right. It is so in those who have been deprived of their right hand in early life; and most persons can do certain things with the left hand better than with the right.” So far, therefore, Dr. Humphry’s decision would appear to be wholly in favour of the conclusion that the superiority of the right hand is an acquired habit. But after stating thus much, he adds: “Though I think the superiority of the right hand is acquired, and is a result of its more frequent use, the tendency to use it in preference to the left is so universal that it would seem to be natural. I am driven, therefore, to the rather nice distinction that, though the superiority is acquired, the tendency to acquire the superiority is natural.”
This “nice distinction” amounts to something very like an evasion of the real difficulty, unlesswe assume Dr. Humphry to mean only what Dr. Buchanan states, that during the weakness of infancy and childhood the two hands are used indiscriminately; and the preferential use of one side rather than the other does not manifest itself until the muscular system has acquired active development. All the processes by which dexterity in the manipulation and use of tools is manifested, are acquired, whether the right or the left hand be the one employed. Men are not born, like ants, bees, spiders, martins, and beavers, with carpentering, weaving, modelling, and architectural instincts, requiring no apprenticeship or culture; though the aptitude in mastering such arts is greater in some than in others. If the tendency in their practice to use the right hand is natural, that is to say, innate or congenital, then there need be no nice distinctions in affirming it. But on any clearly defined physiological deductions of right-handedness from the disposition of the organs of motion or circulation, or any other uniform relation of the internal organs and the great arteries of the upper limbs, left-handedness becomes mysterious, if not inexplicable, unless on the assumption of a corresponding reversal of organic structure; for Dr.Humphry’s assertion that “in all persons the left hand may be trained to as great expertness and strength as the right,” is contradicted by the experience of left-handed persons in their efforts to apply the same training to the right hand.
To the most superficial observer it is manifest that the anatomical disposition of the vital organs is not symmetrical. The heart lies obliquely, from above downwards, and from right to left; the trachea is on the right side, and the right and left subclavian veins and arteries are diversely arranged. There are also three lobes of the right lung, and only two of the left; and the liver is on the right side. Here, therefore, are sources of difference between the right and left sides of the body, which, if subject to variation, offer a possible explanation of the phenomenon that has so long baffled physiologists. To the variations in the disposition of those organs attention has accordingly been repeatedly directed; as in the occasional origin of the left subclavian artery before the right, which, as hereafter noted, Professor Hyrtl suggested as the cause of the transfer of dexterity to the left limb. But instances have repeatedly occurred of the entire transposition of the viscera. “There are men born,” says Dr. Buchanan,“who may grow up and enjoy perfect health, in whom the position of all the thoracic and abdominal viscera is reversed. There are three lobes of the left lung and only two of the right; the liver is on the left side, and the heart is on the right; and so forth.” Those and other malformations, as well as pathological lesions, especially if they occur in early life, may affect the relative power of the two sides; and Dr. Buchanan at a later date reported a case that came under his own notice, in which the entire transposition of the viscera coexisted with left-handedness. But he had already adopted the mechanical theory, subsequently modified, as explained above; and it is only in a closing remark in his paper of 1862 that he makes a passing reference to this remarkable coincidence.
Professor Hyrtl of Vienna, the eminent anatomist already referred to, in discussing the cause of left-handedness in hisHandbuch der Topographischen Anatomie(1860), affirms a correspondence between the ratio of left-handed persons and the occurrence of certain deviations from the normal arrangements of the blood-vessels. “It happens,” he says, “in the proportion of about two in a hundred cases, that the left subclavian artery has its originbeforetheright, and in these cases left-handedness exists, as it also often actually does in the case of complete transposition of the internal organs; and it is found that the proportion of left-handed to right-handed persons is also about two to one hundred.” Professor Hyrtl thinks that ordinarily the blood is sent into the right subclavian under a greater pressure than into the left, on account of the relative position of these vessels; that in consequence of the greater supply of blood, the muscles are better nourished and stronger; and that therefore the right extremity is more used. In cases of anomalous origin of the left subclavian, etc., the reverse occurs, and therefore the left hand is employed in preference. The theory of Professor Hyrtl has this feature to recommend it, that it assigns a cause for the prevalent habit, which, if confirmed, would equally account for the exceptional left-handedness; and no proffered solution of the question, founded on organic structure, is deserving of attention which fails to do so. But the statistics of such internal organic structure are not, like those of the transposition of the heart and immediately related organs, accessible in the living subject, unless in very rare exceptions; and the occurrence of one or two cases in which the deviationfrom the normal arrangement of the artery, or the entire transposition of the viscera, is found to coexist with left-handedness, may only be misleading.
A correspondent ofNature(9th June 1870) refers to a case of transposition of the origin of the right subclavian artery, disclosed by the occurrence of aneurism, where the person was ascertained to have been undoubtedly right-handed. In the following year an interesting article by Dr. Pye-Smith appeared in theGuy’s Hospital Reports, and was subsequently reprinted, with additions, under the title of “The connection of Left-handedness with transposition of Viscera and other supposed anatomical causes.” In this the author states that he found the deviation from the normal arrangement of the primary branches of the aorta, in which the right subclavian arises from the third part of the aortic arch, to occur four times in 296 dissections. As this variation, he says, “cannot be recognised during life, its connection with left-handedness is not easy to investigate. But in one case, at least, Dr. Peacock ascertained for me that the subject of this abnormality, whose heart and arteries he had examined for another purpose, was right-handed during life.” Any one can tell onwhich side his heart lies; but the disposition of the subclavian artery is wholly beyond his cognisance; and, indeed, Professor Hyrtl, while referring to this abnormal organisation as one probable cause of left-handedness, does not affirm more than that the one has been ascertained in some cases to be an accompaniment of the other. The evidence that in other cases it has been unaccompanied by left-handedness shows that it is no necessary source of deviation from normal action.
The other theory, that left-handedness is an inevitable accompaniment of the transposition of the viscera, is more easily tested. It is one that has been repeatedly suggested; and has not only received the sanction of Professor Hyrtl, but is supported by some undoubted cases in which the two conditions coexisted. But, as Dr. Pye-Smith remarks, “a few such instances only prove that transposition of the viscera does notpreventthe subject of the abnormality from being left-handed. Though attention has hitherto been little drawn to this point, there are enough cases already recorded to show that for a person with transposed viscera to be left-handed is a mere coincidence.” In confirmation of this, Dr. Pye-Smith refers to four cases,one of which came under his own observation in Guy’s Hospital, where the subjects of the abnormal disposition of the viscera had been right-handed. In theRochester(N.Y.)Expressof October 1877 a notice appeared of an autopsy on the body of George Vail, of Whitby, Ontario, who had recently died in the Rochester Hospital. Dr. Stone, as there stated, “noticed upon the first examination, when the patient came for treatment, that there was what is technically called ‘juxtaposition of the heart,’ which is a very rare condition. He was gratified at the autopsy to have his diagnosis confirmed, the heart being found on the right side of the body instead of the left.” I immediately wrote to Whitby, and in reply was informed that no one had ever noticed in Vail any indication of his being left-handed. A similar case of the transposition of the viscera, in which, nevertheless, the person was right-handed, recorded by M. Géry, is quoted in Cruveillier’sAnatomie(i. 65). Another is given by M. Gachet, in theGazette des Hospitaux, 31st August 1861; and a third in thePathological Transactions, Vol. XIX. p. 147 (Nature, 28th April 1870). This evidence suffices to prove that there is no true relation between the transpositionof the viscera and left-handedness. Dr. Struthers has shown that “as far as the viscera alone are concerned, the right side is at least 22³⁄₄ ounces heavier than the left, and that this is reduced 7³⁄₄ ounces by the influence of the contents of the stomach, leaving a clear preponderance of at least 15 ounces in favour of the right side.” The preponderance of the right side, he adds, is probably considerably greater than 15 ounces, and it is rendered still more so in the erect posture. The total weight of viscera on the right side he states at 50³⁄₄ ounces, while that of the left side is only 28 ounces, giving a visceral preponderance on the right side of 22³⁄₄ ounces. But if this relative excess of weight on the right side be the true source of right-handedness, the transposition of the viscera ought to be invariably accompanied with a corresponding change. A single example of the preponderant cause, unaccompanied by the assumed effect, is sufficient to discredit the theory.