SIR CHARLES BELL ON THE ORGANS OF THE HUMAN VOICE. 309 
same degree of pressure will be transmitted to every part of the surface of the 
reservoir, equal in magnitude to the base of the piston. And on the contrary, 
supposing the power to be employed on the reservoir for the purpose of raising 
the piston, it would require the weight of a pound on every portion of the 
superficies of the reservoir, equal in extent to the base of the piston, to raise 
the piston with a force of one pound. 
We cannot fail to notice the effect of this law on the cavities of the animal 
body, in diminishing the power of muscular bags in proportion to their in¬ 
creased capacity. 
Elastic fluids are subject to a similar influence, from the pressure extending 
in every direction, and the resistance always being equal to the pressure. 
A man standing on the hydraulic bellows, raises himself by blowing into 
the tube : and contrariwise, the weight of his body does not produce from that 
tube a blast of air superior to the force of contraction of his cheeks. A very 
slight pressure against the nozzle of the common bellows will resist the com¬ 
pression by the handles; and by blowing into the nozzle, we may raise a great 
weight placed on the boards. To reconcile us to the influence of this prin¬ 
ciple, as applicable to the animal economy, we shall take an example before 
applying it to our present subject. 
A sailor leaning his breast over a yard-arm, and exerting every muscle on 
the rigging, gives a direction to the whole muscular system, and applies the 
muscles of respiration to the motions of the trunk and arms, through the in¬ 
fluence of a small muscle that is not capable of raising a thousandth part of 
the weight of his body. He raises himself by the powerful combination of 
the muscles of the abdomen, chest and arms ; but these muscles are controuled 
and directed by the action of a muscle which does not weigh five grains. The 
explanation is this;—a man preparing for exertion, draws his breath and ex¬ 
pands his chest. But how is this dilatation to be maintained ? if the muscles 
which expand the chest are to continue in exertion to preserve it so, there 
must be a great expenditure of vital force; besides, these muscles are now 
wanted for another office. The small muscle that closes the chink of the glottis 
suffices. It contracts on the extremity of the windpipe; and here, acting so 
as to confine the column of air, it is superior to the united power of all the 
muscles of the chest and trunk of the body which act upon the cavity of the 
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