13 
of the Heart and Arteries. 
second, its greatest velocity must be about three times as 
much, since the contraction of the heart is supposed to occupy 
only about one third part of the interval between two succes- 
sive pulsations ; and if the velocity of the pulse is sixteen feet 
in a second, that of the blood itself must be about one eighth 
part as great ; so that the column of blood occupying eight 
inches may occupy only seven ; hence the diameter must in- 
crease in the ratio of about fifteen to sixteen. The tension 
will also become one eighth greater, and the force of the 
heart must be capable of supporting a column of one hundred 
and one inches. This force would, however, require to be 
somewhat increased, from the consideration that the force re- 
quired at the end of any canal during the reflection of a pul- 
sation or wave of any kind, is twice as great as the force 
exerted during its transmission, and the force employed in the 
origination of a wave or pulse in a quiescent fluid, is the same 
as is required for its reflection ; on the other hand, a weaker 
pulsation, proceeding into a narrower channel, becomes more 
energetic, so that, from this consideration, a force somewhat 
smaller would be required in the heart : on the whole, how- 
ever, it appears probable, that the former of these corrections 
must be the more considerable, and that the force of the heart 
must be measured by the pressure of a column, rather more 
than less than one hundred and one inches high : nor would 
this force by any means require a strong exertion of muscular 
power ; for it only implies a tension of something less than 
three pounds for each inch of the circumference of the great- 
est section of the heart ; and supposing the mean thickness 
half an inch, an equal number of the fibres of some other 
muscles of the body would be capable of exerting a force of 
