of the Heart and Arteries. 17 
is almost universally believed. The arguments, which may 
be employed to prove this, are nearly the same that I have 
already stated, in examining the motion of a fluid, carried along 
before a moving body in an open canal ; but in the case of an 
elastic tube, the velocity of the transmission of an impulse 
being rather diminished than increased by an increase of ten- 
sion, the reasoning is still stronger and simpler ; for it may 
here be safely asserted, that the anterior parts of the dilatation, 
which must be forced along by any progressive contraction 
of the tube, can only advance with the velocity appropriate to 
the tube, and that its capacity must be proportionate to its length 
and to the area of its section : now the magnitude of its section 
must be limited by that degree of tension which is sufficient to 
force back through the contraction what remains of the dis- 
placed fluid, and the length by the difference of the velocity 
appropriate to the tube, and that with which the contraction 
advances ; consequently if the contraction advance with the 
velocity of a pulsation, as any contractile action of the arte- 
ries must be supposed to do, this length necessarily vanishes, 
and with it the quantity of the fluid protruded ; the whole 
being forced backwards, by the distending force which is ex- 
erted by a very small dilated portion, immediately preceding 
the contraction. It might indeed be imagined, that the con- 
traction follows the pulsation with a velocity somewhat smaller 
than its own ; but this opinion would stand on no other foun- 
dation than mere conjecture, and it would follow, that the 
pulse would always become more and more full, as it became 
more distant from the heart ; of which we have nothing like 
evidence: nor would a moderate contraction, even if this 
supposition were granted, produce any material effect. For 
MDCCCIX. D 
