(Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus)
By William Harvey
The original, squashed down to read in about 20 minutes
William Harvey of Folkestone studied medicine at Padua in Italy under the pioneering surgeon Hieronymus Fabricius, who had discovered the one-way valves in veins. Harvey solved the mystery of their function and succeeded in explaining the circulation of blood through the body by the heart through its alternate diastole (expansion) and systole (contraction). He was the first to suggest that mammals reproduced by the fertilisation of an egg by sperm. So accepted are his discoveries now that it seems remarkable that neither was universally believed in his own time.
To The Most Illustrious And Indomitable Prince Charles King Of Great Britain, France, And Ireland. Defender Of The Faith.
I: MOTIONS OF THE HEART IN LIVING ANIMALS
When first I gave my mind to vivisections as a means of discovering the motions and uses of the heart, I found the task so truly arduous that I was almost tempted to think, with Fracastorius, that the motion of the heart was only to be comprehended by God. For I could neither rightly perceive at first when the systole and when the diastole took place, nor when and where dilation and contraction occurred, by reason of the rapidity of the motion, which, in many animals, is accomplished in the twinkling of an eye, coming and going like a flash of lightning.
At least it appears that these things happen together or at the same instant: the tension of the heart, the pulse of its apex, which is felt externally by its striking against the chest, the thickening of its walls, and the forcible expulsion of the blood it contains by the constriction of its ventricles.
Hence the very opposite of the opinions commonly received appears to be true; inasmuch as it is generally believed that when the heart strikes the breast and the pulse is felt without, the heart is dilated in its ventricles and is filled with blood. But the contrary of this is the fact; that is to say, the heart is in the act of contracting and being emptied. Whence the motion, which is generally regarded as the diastole of the heart, is in truth its systole.
And in like manner the intrinsic motion of the heart is not the diastole but the systole; neither is it in the diastole that the heart grows firm and tense, but in the systole; for then alone when tense is it moved and made vigorous. When it acts and becomes tense the blood is expelled: when it relaxes and sinks together, it receives the blood in the manner and wise which will by and by be explained.
From divers facts it is also manifest in opposition to commonly received opinions, that the diastole of the arteries corresponds with the time of the heart's systole; and that the arteries are filled and distended by the blood forced into them by the contraction of the ventricles. It is in virtue of one and the same cause, therefore, that all the arteries of the body pulsate, viz. the contraction of the left ventricle in the same way as the pulmonary artery pulsates by the contraction of the right ventricle.
I am persuaded it will be found that the motion of the heart is as follows: First of all the auricle contracts and throws the blood into the ventricle, which being filled, the heart raises itself straightway, makes all its fibres tense, contracts the ventricles and performs a beat, by which beat it immediately sends the blood supplied to it by the auricle into the arteries; the right ventricle sending its charge into the lungs by the vessel called the vena arteriosa, but which, in structure and function, and all things else is an artery; the left ventricle sending its charge into the aorta, and through this by the arteries to the body at large.
The grand cause of hesitation and error in this subject appears to me to have been the intimate connexion between the heart and the lungs. When men saw both the pulmonary artery and the pulmonary veins losing themselves in the lungs, of course it became a puzzle to them to know how the right ventricle should distribute the blood to the body or the left draw it from the venae cavae.
Or they have hesitated because they did not perceive the route by which the blood is transferred from the veins to the arteries, in consequence of the intimate connexion between the heart and lungs. And that this difficulty puzzled anatomists not a little when in their dissections they found the pulmonary artery and left ventricle full of black and clotted blood, plainly appears when they felt themselves compelled to affirm that the blood made its way from the right to the left ventricle by sweating through the septum of the heart.
Had anatomists only been as conversant with the dissection of the lower animals as they are with that of the human body, the matters that have hitherto kept them in perplexity of doubt would, in my opinion, have met them freed from every kind of difficulty. And first in fishes, in which the heart consists of but a single ventricle, they having no lungs, the thing is manifest. Here the sac, which is situated at the base of the heart, and is the part analogous to the auricle in man, plainly throws the blood into the heart, and the heart in its turn conspicuously transmits it by a pipe or artery, or vessel analogous to an artery; these are facts which are confirmed by simple ocular experiment. I have seen, further, that the same thing obtained most obviously.
And since we find that in the greater number of animals, in all indeed at a certain period of their existence, the channels for the transmission of the blood through the heart are so conspicuous, we have still to inquire wherefore in some creatures, those, namely, that have warm blood and that have attained to the adult age, man among the number, we should not conclude that the same thing is accomplished through the substance of the lungs, which, in the embryo, and at a time when the functions of these organs is in abeyance, nature effects by direct passages, and which indeed she seems compelled to adopt through want of a passage by the lungs; or wherefore it should be better (for nature always does that which is best) that she should close up the various open routes which she had formerly made use of in the embryo, and still uses in all other animals; not only opening up no new apparent channels for the passage of the blood, therefore, but even entirely shutting up those which formerly existed in the embryos of those animals that have lungs.
For while the lungs are yet in a state of inaction, nature uses the two ventricles of the heart as if they formed but one for the transmission of the blood. The condition of the embryos of those animals which have lungs is the same as that of those animals which have no lungs.
Thus, by studying the structure of the animals who are nearer to and farther from ourselves in their modes of life and in the construction of their bodies, we can prepare ourselves to understand the nature of the pulmonary circulation in ourselves, and of the systemic circulation also.
II: SYSTEMIC CIRCULATION
What remains to be said is of so novel and unheard-of a character that I not only fear injury to myself from the envy of a few, but I tremble lest I have mankind at large for my enemies, so much do wont and custom that become as another nature, and doctrine once sown that hath struck deep root, and respect for antiquity, influence all men.
And, sooth to say, when I surveyed my mass of evidence, whether derived from vivisections, and my previous reflections on them, or from the ventricles of the heart and the vessels that enter into and issue from them, the symmetry and size of these conduits-for nature, doing nothing in vain. would never have given them so large a relative size without a purpose; or from the arrangement and intimate structure of the valves in particular and of the many other parts of the heart in general, with many things besides; and frequently and seriously bethought me and long revolved in my mind what might be the quantity of blood which was transmitted, in how short a time its passage might be effected and the like; and not finding it possible that this could be supplied by the juices of the ingested aliment without the veins on the one hand becoming drained, and the arteries on the other getting ruptured through the excessive charge of blood, unless the blood should somehow find its way from the arteries into the veins, and so return to the right side of the heart: when, I say, I surveyed all this evidence, I began to think whether there might not be a motion as it were in a circle.
Now this I afterwards found to be true; and I finally saw that the blood, forced by the action of the left ventricle into the arteries, was distributed to the body at large, and its several parts, in the same manner as it is sent through the lungs, impelled by the right ventricle into the pulmonary artery: and that it then passed through the veins and along the vena cava, and so round to the left ventricle in the manner already indicated.
For the moist earth, warmed by the sun, evaporates; the vapours drawn upwards are condensed, and descending in the form of rain moisten the earth again. And by this arrangement are generations of living things produced; in like manner, too, are tempests and meteors engendered by the circular motion of the sun. The various parts of the body are nourished and quickened by the warmer, more perfect, vaporous, spirituous and, as I may say, alimentive blood; which, on the contrary, in contact with these parts becomes cooled, coagulated and, so to speak, effete; whence it returns to its sovereign the heart, as if to its sources, or to the inmost home of the body, there to recover its state of excellence or perfection. Here it resumes its due fluidity, receives an infusion of natural heat and is impregnated with spirits, and hence it is again dispersed.
III: CONFIRMATIONS OF THE THEORY
Three points present themselves for confirmation, which, being established, I conceive that the truth I contend for will follow necessarily and appear as a thing obvious to all.
The first point is this. The blood is incessantly transmitted by the action of the heart from the vena cava to the arteries in such quantity that it cannot be supplied from the ingesta, and in such wise that the whole mass must very quickly pass through the organ. Let us assume the quantity of blood which the left ventricle of the heart will contain when distended to be, say, two ounces (in the dead body I have found it to contain upwards of two ounces); and let us suppose, as approaching the truth, that the fourth part of its charge is thrown into the artery at each contraction. Now, in the course of half an hour the heart will have made more than one thousand beats. Multiplying the number of drachms propelled by the number of pulses, we have one thousand half-ounces sent from this organ into the artery; a larger quantity than is contained in the whole body.
This truth, indeed, presents itself obviously before us when we consider what happens in the dissection of living animals. The great artery need not be divided, but a very small branch only (as Galen even proves in regard to man), to have the whole of the blood in the body, as well that of the veins as of the arteries, drained away in the course of no long time-some half hour or less.
The second point is this. The blood, under the influence of the arterial pulse, enters, and is impelled in a continuous, equable and incessant stream through every part and member of the body in much larger quantity than were sufficient for nutrition, or than the whole mass of fluids could supply.
I have here to cite certain experiments. Ligatures are either very tight or of middling tightness. A ligature I designate as tight, or perfect, when it is drawn so close about an extremity that no vessel can be felt pulsating beyond it. Such ligatures are employed in the removal of tumours: and in these cases, all afflux of nutriment and heat being prevented by the ligature, we see the tumours dwindle and die, and finally drop off.
Now let anyone make an experiment upon the arm of a man, either using such a fillet as is employed in blood-letting, or grasping the limb lightly with his hand: let a ligature be thrown about the extremity and drawn as tightly as can be borne. It will be perceived that beyond the ligature the arteries do not pulsate, while above it the artery begins to rise higher at each diastole and to swell with a kind of tide as if it strove to break through and overcome the obstacle to its current. Then let the ligature be brought to that state of middling tightness which is used in bleeding, and it will be seen that the hand and arm will instantly become deeply suffused and extended, and the veins show themselves tumid and knotted.
Which is as much as to say that when the arteries pulsate the blood is flowing through them, but where they do not pulsate they cease from transmitting anything. The veins again being compressed, nothing can flow through them; the certain indication of which is that below the ligature they are much more tumid than above it.
Whence is this blood? It must needs arrive by the arteries. For that it cannot flow in by the veins appears from the fact that the blood cannot be forced towards the heart unless the ligature be removed.
Further, when we see the veins below the ligature instantly swell up and become gorged when from extreme tightness it is somewhat relaxed, the arteries meanwhile continuing unaffected, this is an obvious indication that the blood passes from the arteries into the veins and not from the veins into the arteries, and that there is either an anastomosis of the two orders of vessels, or pores in the flesh and solid parts that are permeable to the blood. And now we understand wherefore in phlebotomy we apply our fillet above the part that is punctured, not below it. Did the flow come from above, not from below, the bandage in this case would not only be of no service, but would prove a positive hindrance.
And further, we perceive that a circulation is absolutely necessary, seeing that the quantity of blood cannot be supplied immediately from the ingesta, and is vastly more than can he requisite for the mere nutrition of the parts.
That the veins return this blood to the heart incessantly from all parts and members of the body will be made clear from the valves which are found in the cavities of the veins themselves, from the uses of these and from experiments cognisable by the senses. The celebrated Hieronymus Fabricius first gave representations of the valves in the veins. Their office is by no means explained when we are told that it is to hinder the blood, by its weight, from flowing into inferior parts; for the edges of the valves in the jugular veins hang downwards, and are so contrived that they prevent the blood from rising. The valves, in a word, do not invariably look upwards, but always towards the trunks of the veins- towards the seat of the heart. They are solely made and instituted lest, instead of advancing from the extreme to the central parts of the body the blood should rather proceed along the veins from the centre to the extremities: but the delicate valves, while they readily open in the right direction, entirely prevent all such contrary motion, being so situated and arranged that if anything escapes, it is immediately received on the convexity of the one beneath, which is placed transversely with reference to the former, and so is hindered from getting any farther.
And this I have frequently experienced in my dissections of veins. If I attempted to pass a probe from the trunk of the veins into one of the smaller branches, whatever care I took I found it impossible to introduce it far any way by reason of the valves; whilst it was most easy to push it along in the opposite direction. from without inwards, or from the branches towards the trunks and roots. And now I may be allowed to give my view of the circulation of the blood, and to propose it for general adoption.
IV: THE CONCLUSION
Since all things, both argument and ocular demonstration, show that the blood passes through the lungs and heart by the action of the ventricles; and is sent for distribution to all parts of the body, where it makes its way into the veins and pores of the flesh; and then flows by the veins from the circumference on every side to the centre, from the lesser to the greater veins: and is by them finally discharged into the veini cuvii and right auricle of the heart, and this in such a quantity or in such a flux and reflux, thither by the arteries, hither by the veins, as cannot possibly be supplied by the ingesta, and is much greater than can be required for mere purposes of nutrition; therefore, it is absolutely necessary to conclude that the blood in the animal body is impelled in a circle and is in a state of ceaseless motion; and that this is the act, or function, which the heart performs by means of its pulse, and that it is the sole and only end of the motion and contraction of the heart. For it would be difficult to explain in any other way to what purpose all is constructed and arranged as we have seen it to be.
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