180 



KNOWLEDGE 



[Dec. :50, 1881. 



RIGHT-HANDEDNESS. 



Bt .Tamks Shaw. 



THERE is ft difference both in structure and capacity bctwrcu 

 Iho left and the riKht lun^. The former has two lobcH, the 

 latter bus three. Suppose 240 inches of air have been inUaluil, 

 about 130 have been taken into the ri^ht lung, and 110 into the left. 

 Watch at tho name time the riRht sido of the chest, and it will bo 

 gcen to bo mciro bulged out during inspiration. Meanwhile, the 

 lower ribs, as tlioy roredo from an imaginary middle line, aro firndy 

 bound by a ligament, or short cord, to the liver. Tho liver, a 

 heavy organ of ubont 4 lb. weight, inclines tho centre of gravity to 

 the side to which it swings, and tho greater expansion of the right 

 Inng and the shifting of the liver to tho right aide tend to shift tho 

 centre of gravity to that side. 



Tho heart, li'rmly attached to tho spine and midriff, rcTnains 

 immoveable, but the stomach and spleen incline to follow tho liver. 

 'J'hey cannot follow tho left ribs in a contrary direction, for they 

 are not joined to them. The shifting of the lino containing the 

 centre of gravity towards the right has no countervailing-force 

 opposed to it, for although the greater part of tho heart and the 

 spleen is on the left side, it is not enough to balance the part 

 carried towards the right by tho descent of the diaphragm, daring 

 nspiration. 



It has been estimated that tbe viscera of the abdomen and tho 

 chest weigh heavier, by about a jionnd, on the right side than the 

 left. Now it must be plain that if the right side be heavier 

 naturally, and still heavier during the inspiration that precedes 

 effort, tho foot that supports it will be more leant upon ; and if we 

 loan more upon the right foot, it will afford a steadier basis of action 

 for the right arm than for tho left. According to this view, first 

 clearly put fortli by Professor Buchanan, there is a mechanical 

 reason for right-handedness. Tlie right leg is first preferred and 

 utilised in action, and upon this preference the right hand and 

 arm come more readily into use, and are then taken up con- 

 sciously and educated as the skilled limb. No sooner is a beginning 

 made of preference than the muscles oftenest or most strenuously 

 used get stronger. 



Violently exercise the right hand and arm, and you might expect 

 that both lungs would inflate to their uttermost. But this is not the 

 case. The right Inng is better filled with air in proportion to its 

 capacity than the left. If we exercise tho left arm, tbe left lung is 

 more inflated, according to capacity, than the right. Wo may even 

 ivitness the right cheek of a man, violently engaged in lifting a load 

 with the right hand and .arm, inflating unconsciously. In some 

 jihysical efforts, such as throwing a stone, in which the centre of 

 gravity advances from tho right, fonvard, and towards the left, 

 the dilation of both check and lung has been observed, passing over 

 from tho right to the left. Tho temptation to prefer the right 

 shoulder, the right arm and hand, in lifting a dead weight, because 

 of the centre of gravity being more nearly over the right foot than 

 over tho left, is quite a natural one. So, when a carter puts his 

 shoulder under the shaft of his cart, he prefers to hoist it up with 

 tho right shoulder, as having more power in raising it. 



But the question m.iy be urged, why are burdens gener,ally carried 

 on the left '< Although portable loads are generally placed on the 

 left shoulder, thii?, instead of being at variance with the mechanical 

 theory, is really a proof of it. When a man has a hea^■y weight 

 upon his left shoulder, the burden is, in reality, borne by tho right 

 rather than by tho left lower limb. The body is inclined to the 

 right, so that the mechanical axis passes from the left shoulder to 

 the right foot, and tho load is retained over it by the help of the 

 right arm. In tho case of burdens, such as fishwives' baskets, 

 borne on the left side, it must be remembered that as tho right side 

 is the heavier, these burdens help to restore equilibrium with less 

 of a bend towards tho opposite side, and so leave the motion of tho 

 limbs less constrained. This is probably one of the causes why a 

 nurse carries her child in her left arm. although we must recollect 

 that, by doing so, she has another advantage, namely, the freedom 

 of the right hand for work. 



Professor Perrier informs us that the brain has a cross action. 

 The left hemisphere governs tho right side, and the right hemisphere 

 governs the left side. Therefore, when wo see with our right eye, 

 we see with the left side of our brain, and when wo see with our 

 left eye, we see with tho right aide. Now, not only has the right 

 side a mechanical advantage; but it is strongly suspected 

 that tho left hemisphere of tho brain, which governs tho 

 movement of tho right side muscles, is, so to speak, a batteiy 

 of greater power than the right hemisphere. Dr. Boyd made 

 observations on the patients in St. Magdalen's Hospital, and he sets 

 forward as a cnrious result, that, after weighing separately the 

 hemispheres of 200 indiviil-uals. almost invariably tho left hemisphere 

 exceeded by an ounce the weight of the right hemis}>here. To do 



so exactly, bowovor, reqairca groat nicety, aa there is no deftnit* 

 division between the two hemispheres ; and so wc arc not surprised 

 that in Dr. Wagner's experience tho proportion of cases having 

 heavier left lobes wiui as five to two. In the Iteport of St. George's 

 Hospital (1S69), there is recorded a case of loss of speech and 

 paralysis of tho left arm of a left-handed lad, whose brain, after 

 death, exhibited a softening of the right homisphore. The question 

 of how much tho strength and dexterity of the right hand depends 

 on the shape and nature of the brain substance is beset with difficul- 

 ties ; but the balance of the eWdcnce is in favour of the constitution of 

 the brain itself being a reason in favour of right-hand predominance. 

 A reason founded on nature is much more satisfactory than the 

 notion, somewhat prevalent, that right-handedness is a fashion. 

 True, there is a percentage of our fellow-creatures left-handed; 

 and there is a diliiculty to account for this peculiarity. Bat it ia 

 not easy to account for many peculiarities equally striking ; such as 

 tho want of beard in some men ; the greater or less number of teeth, 

 toea, and fingers ; tho heart being found occasionally on the right 

 side ; and the transposition of the viscera. Some men can shut one 

 eye and keep the other open at the same time. Others can only do 

 so with difficulty ; and others, again, aro quite unable to do so. 

 From the evolutionist's point of view, it seems to me as if our 

 destiny were to become more intensely and more generally 

 right-handed than we are. If we go far enough back in 

 infant biography, we arrive at a period when locomotion is 

 chiefly performed by tho aid of all four limbs. This is the case 

 with adult apes and monkeys, who shamble along on a plain, or 

 climb more gracefully in the woods, by tho aid of all their limbs. 

 With the infant, the difference of internal structure — throwing the 

 centre of gravity to the right — is scarcely perceptible. 



It is argued by some writers that it would be a gfreat advantage 

 were we ambidexter, using both hands with like skill. Now, no one 

 doubts that the specialisation of hands for the purpose of grasping, 

 and feet for locomotion, is of more advantage to man, than if he 

 had four hands fitted for both functions. As the child grows older, 

 the difference of hands appears; and this difference, in all civilised 

 countries, is eagerly helped by precept and example. As in playing 

 whist, it is better that partner should have many trump cards and 

 self few, than that each should have an average number ; so it is 

 found that in a world where time is so valuable, where art is long 

 and life is short, it is better one hand should be verj- well educated 

 and the other comparatively neglected, than that each should have 

 a moderate aptitude. 



We can go back, in imagination, to the time when the grasping 

 of a stick or stone was all the education received by a human hand. 

 We can suppose the make of the body at that time more symmetri- 

 cal, as an infant's is with us now. It is like going back to the time 

 when the ancestors of our horses had more of a normal foot — three 

 toes, instead of the one toe of our present steeds. Right-handedness 

 would not be so regular nor so apparent then; just as it is said to 

 bo with Fijians at the present day, or, as it has been observed 

 with the African elephant, which has a tusk called the " servant," 

 with whch it burrows more freely, but which is not so regularly the 

 right tusk as the working hand ia the right one with us. As soon, 

 however, as man combined, either in labour or in war, the necessity 

 for preferring one hand to the other would become apparent. 

 Indeed, the evident advantage of shielding such a vital organ aa 

 tho heart from wounds, and pushing forward the less vital right 

 side, would incline men to place the shield in the left hand and the 

 sword in the right. At all events, tho thickening of complex cir- 

 cumstances would be unfavourable to a state of unstable equilibrium. 

 When once tho movement of preference began, everything would 

 tend to strengthen it. Many of the implements by which man con-a 

 quers nature would require to be made either to suit the supinatingl 

 motion of the right hand or of the left. ■ 



The slightly stronger side would gain the day, and become the 

 more apt and stronger after it had gained it. Now, since it has 

 become an accomplislied fact that screws, gimlets, seJAors, scythes, 

 Ac, are all made for right-handed men, he who woulTcducate us to 

 the ambidexter must have two handles on every door, two methods 

 of winding up every watch, Janus-shaped carpenters' benches and 

 printouttors' gauges, duplicate sets of screw-nails, scissors and 

 scythes. 



Not only is the right hand the most dextrous, but, as far as I have 

 extended my observations, in those cases in which there is a dif- 

 ference in the strength of vision between the right and the left eye, 

 the advantage, more frequently, lies with the former. It may be 

 thought that investigations of this kind aro unpractical, but it will 

 not appear so when it :s stated that they have been the means of 

 discovering serious differences in the organs of vision of the same 

 individual, which drawbacks can be greatly modified by the spec- 

 tacles of the optician. The relief, in reading, given to such a lop- 

 eyed person when he has got a lens suited to either eye, is so great 

 that, when on«e discovered, it is never forgotten. It is wonderful 



