i6 Dr. Young’s Lecture on the Functions 
actual pressure in the arteries of a dog, the remaining one 
hundred and eighty five feet will give a velocity of at least 
fifty four feet in a second, for the propagation of the pulse in 
the dog. It is not however ascertained, that all the membranes, 
which may have surrounded the artery in this experiment, are 
called into action in its ordinary pulsation, much less that the 
force, developed by their tension, varies precisely according to 
the general law of perfectly elastic bodies : but this mode of 
calculation is still amply sufficient to make it probable, that 
the velocity of the pulsations, in the larger arteries, must 
amount to at least forty feet in a second, although some very 
considerable deductions must be made, on account of the resis- 
tances of various kinds, which cannot be comprehended in the 
calculation. 
The artery must not be supposed to subside, immediately 
after each pulsation, precisely to its original dimensions, since 
it must remain somewhat fuller, in order to supply the capil- 
lary arteries, and the veins, in the interval between the two 
successive pulsations : and in this respect it differs from the 
motions of a wave through a canal, which is open on both 
sides : but the difference may be understood, by supposing a 
partial reflection of the pulse to take place at every point 
where it meets with any resistance, which will leave a general 
distension of the artery, without any appearance of a retro- 
grade pulsation. 
I shall proceed to inquire, in the third place, into the nature 
and extent of the functions which are to be attributed to the 
muscular fibres of the coats of the arteries ; and I apprehend 
that it will appear to be demonstrable, that they are much 
less concerned in the progressive motion of the blood, than 
