THE CIRCULATION OF THE BLOOD DEPENDS. 
493 
sibly affected by the heart’s ceasing to beat ; nor does this arise from some 
imperceptible impulse still given by the heart, because when all the vessels 
attached to this organ are secured by a ligature and the heart cut out, the 
result is the same. 
That the circulation in the capillary vessels is independent of the heart, may 
be shown by various other means. On viewing the motion of the blood in 
them, with the assistance of the microscope, it may generally be observed that 
it is moving with different degrees of velocity in the different vessels of the 
part we are viewing, frequently more than twice as rapidly in some than in 
others. Were the motion derived from a common source, this could not be 
the case. It is impossible, in the motion of the blood in the capillaries, in the 
least degree to perceive the impulse given by the beating of the heart, which 
causes the blood in the arteries to move more or less per saltum, the motion of 
the blood in the former being uniform as long as they retain their vigour, and 
the necessary supply of blood is afforded from the larger vessels. I have found 
by experiments very frequently repeated*, that the motion of the blood may 
be accelerated or retarded in the capillaries by stimulants or sedatives, acting 
not through the medium of the heart, but on these vessels themselves. Nay, 
so little effect has the action of the heart on the motion of the blood in the 
capillaries, that I have found that when the power of the capillaries of a part 
is suddenly destroyed by the direct application of opium to them, the motion 
of the blood in them instantly ceases, although the vigour of the heart and 
that of every other part of the sanguiferous system is entire 
If the circulation in the capillaries be thus independent of the heart, it is 
evident that the influence of that organ cannot extend to the veins. On com- 
paring the whole of the foregoing circumstances, is it not a necessary infer- 
ence that, the motion of the blood in the veins, like that in the capillaries, de- 
pends on the power of these vessels themselves ? But that we may not trust 
to any train of reasoning, where it is possible to have recourse to direct proof, 
I made the following experiment, with the assistance of Mr. Cutler. 
Exp. — In the newly dead rabbit, in which the circulation was maintained by 
artificial respiration, the jugular vein was laid bare for about an inch and a 
half ; a ligature was then passed behind the part of the vessel nearest to the 
* My Treatise on the Vital Functions. t Ibid. 
