The circulation of the blood was first taught by the unfortunate Servetus
in 1553, who was burnt to death as a heretic; and, a century afterwards,
demonstrated by our Harvey, who is justly considered as having discovered
the wonderful mechanism of the motion of the vital fluid.
There is no doubt, however, that the ancients had formed, if not a
correct, at least an ingenious, idea of it. Hippocrates tells us "that all
the veins communicate with each other, and flow from one vessel into
others; and that all the veins that are spread over the body carry a flux
and movement originating in a single vessel." He avows that he is ignorant
of the principle whence it arises, or of its termination, it appearing
to be a circle without beginning or end. He further states, that the heart
is the source of the arteries, through which blood is carried over the
body, communicating life and heat; and he adds, that they are so many
rivulets that irrigate the system, and carry vitality into every part: the
heart and veins are in constant motion; and he compares the circulation of
blood to the course of rivers, that return to their source by
extraordinary deviations. He therefore directs blood-letting to restore a
free current of the blood and other spirits in apoplexies and other
diseases of a similar nature, which he attributed to obstruction in the
vessels intercepting the flow of their contents. He also observes, that
when bile enters the blood, it deranges its consistence, and disturbs its
ordinary course towards another point: and he compares the circulation to
balls of thread, the threads of which return to each other in a circuitous
manner, terminating at the point whence their motion arose.
Plato thought that the heart was the source of the veins, and of the
blood, that was rapidly borne to every part of the body. Aristotle tells
us that the heart is the principle and source of the veins and of the
blood. He considered that there were two veins proceeding from this organ,
one from the left side, the other from the right; the first he termed
_aorta_: and he further maintained that the arteries communicated with the
veins, with which they were intimately connected.
Julius Pollux taught, in his _Gnomasticon_, that the arteries are the
channels through which the spirits circulate as the veins propel the
blood; and he describes the heart as having two cavities, one
communicating with the arteries, and the other with the veins. Apuleius
tells his disciples that the heart propels the blood through the lungs, to
be afterwards distributed over the system.
In the writings of Nemesius, bishop of Emissa, we read that the movement
observed in the pulse originates in the heart, chiefly from the artery of
the left ventricle of the viscus. This artery is dilated, and then
contracted, by a constant and powerful harmonious action. When dilated the
vessel draws towards it the most subtile portions of the neighbouring
blood, and the vapour or exhalation of this fluid, that feeds the animal
spirits; but when it contracts, it exhales, through various channels of
the body, all the vapours that it contains.
Strange as it may appear, doubts were once entertained as to the actual
situation of the heart, whether it was lodged in the right or the left
side of the body. The question was finally settled by a professor of
Heidelberg, who for the purpose killed a pig in the presence of the
Margrave of Baden, Durlach, who then laboured under a supposed disease of
that organ, which it was then clearly shown occupied the left side. The
result of this experiment, however proved somewhat detrimental to his
Highness's physician, who was dismissed, although he maintained with all
becoming courtesy and respect, that the heart of his princely master could
not _possibly be_ in the same position as that of a hog.
Michael Servetus, in his work, _De Christianismi restitutione_, also in
the 7th book, _De Trinitate Divina_, for which he was sentenced to the
stake a very short time after its publication, gives us the following
description of this important function: The blood, which is a vital
spirit, is diffused all over the body by _anastomoses_, or inosculation of
two vessels through their extremities. The air in the lungs contributes to
the elaboration of the blood, which it draws for that purpose from the
right ventricle of the heart through the pulmonary artery. This blood is
prepared in the lungs by a movement of the air that agitates it,
subtilizes it, and, finally, mingles it with that vital spirit which is
afterwards retransmitted to the heart by the movement of the diastole, as
a vital fluid proper to maintain life. This communication and preparation
of the blood, he further states, is rendered evident by the union of the
arteries and veins in this organ; and he concludes by affirming that the
heart, having thus received the blood prepared by the lungs, transmits it
through the artery of the left ventricle, or the aorta, to every part of
the body.
Great care was of course taken to destroy this abominable heretical
publication, which was burnt by the common hangman in Geneva, Frankfort,
and several provinces of France. The work thence became so scarce, that it
is said only three or four copies of it are in existence. One of them was
in the library of the Landgrave of Hesse-Cassel.
John Leonicenus relates that the celebrated Paul Sarpi otherwise named Fra
Paolo, had also discovered this circulation, and demonstrated the valves
of the veins, which open to afford a free passage to the blood, and close
to prevent its return. This discovery, it is pretended, was made known to
Fabricius ab Aquapendente, professor of medicine in Padua in the sixteenth
century, and successor of Fallopius, and who communicated the fact to
Harvey, then a student in that university.
Some time before Harvey's discovery, Cesalpinus had described with great
precision the pulmonary circulation; and, on finding that veins swelled
under a ligature, he attributed this enlargement to the warmth of the
blood. This warmth, he says, proceeds from a spirit residing in the blood.
The left ventricle is filled with blood of a spirituous nature; and one
can trace the movement of the blood towards the superior parts, and its
return (_retrocessus_) to the internal ones,--that is to say, a return by
which it comes back from the extremities to the heart, when awake or
sleeping, from every part of the body; for if you tie the vessels, or if
they are obstructed, the current of the blood is stopped, and then their
smaller ramifications tumefy towards their origin. The following are his
words: "Sic non obscurus est ejusmodi motus in quacumque corporis parte,
si vinculum adhibeatur, aut alia ratione occludantur venae: cum enim
tollitur permeatio, intumescunt rivuli qua parte fluere solent." From
these expressions it is clear that Cesalpinus suspected the great
circulation, and had a fair idea of its nature; yet there is no doubt but
that it was to our Harvey that the first demonstration of this wondrous
function was reserved.