28 DANIEL WILSON ON THE RIGHT 
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 preéminence 
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’s “ Mechanical Theory,” Dr. John 
Struthers communicated to the Edinburgh “ Medical Journal,” a 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 the 
right side of the medial line are on on average 2275 oz. av. heavier than those on the left 
side. The right lung, in the male, weighs 24 oz., the left 21, giving a prepondance 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 34 
oz. for the right, and 74 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’ determination of the exact weight and relative eccentri- 
city of the viscera on the two sides of the body was fully recognised by Dr. Buchanan ; 
and in acommuuication 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 toit. 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 ofthe 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 preference to 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 
