he heart divided into right and left hearts by dissection at
the septum: the circulatory system might then be represented by an
endless tube. Let such an one, nine or ten feet in length, and of one
inch bore (to be filled with water) be placed upon a horizontal table.
Let an enlargement of the tube be made by a tin vessel to represent the
lungs, which shall contain about one-fifth part of the water. Let the
tube connected with the right side of the vessel have, at a little
distance from the vessel, a smaller enlargement, composed of
india-rubber, which can be grasped by the hand, to represent the heart's
right ventricle, with a valve on each side opening towards the tin
vessel, the two to represent the tricuspid and semi-lunar valves. Let
the whole be made nearly full of water; then, under the tin vessel
(representing the lungs), let a fire be made. As the water heats, it
will expand; and as the valve closes to the right, it will go off to the
left side of the vessel. But, as no water will come in from the right,
on account of the valves, there will be no current. Now let the hand
grasp the india-rubber, and the fluid between the valves being displaced
by its pressure, all the water will go towards the tin vessel, because,
while the valve representing the tricuspid would close, that
representing the semi-lunar (between the mimic heart and lungs) would
open--and very freely; because the expansion made by the heat under the
tin vessel had created a vacuum, and thus made a suction power to draw
it forward, while there is a driving power behind to force it onward
into the tin vessel. Then relaxing the hand, a vacuum will exist between
the two valves; and the valve in the rear of the current now begun (the
tricuspid) would open, and the water rush in to fill the vacuum in the
india-rubber ventricle, to be again pressed forward by the next grasp of
the hand; and thus--the fire (representing respiration) being kept up,
and the alternate grasping and relaxing of the hand (representing the
heart's regular impulse)--a perpetual circulation might be made to go
on;[1] but not without another condition of the problem.

And it was in performing this experiment that a truth was discovered,
which, had it been known, many who have ignorantly lost their lives
might have preserved them. When the fluid in the apparatus became
equally, or nearly as much, heated at the extreme parts of the
circulating tube as at the heating vessel, then the m