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 that the 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 line with 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 his spade 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 to and 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 very simple 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 use their 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 on The 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, unless we 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 his Handbuch 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 origin before the right, 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 deviation from 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 of Nature (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 the Guy’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 on which 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 not prevent the 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 the Rochester (N.Y.) Express of 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’s Anatomie (i. 65). Another is given by M. Gachet, in the Gazette des Hospitaux, 31st August 1861; and a third in the Pathological Transactions, Vol. XIX. p. 147 (Nature, 28th April 1870). This evidence suffices to prove that there is no true relation between the transposition of 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.