Part 9 (1/2)

CHAPTER XIII

THE THIRD POSITION IS CONFIRMED: AND THE CIRCULATION OF THE BLOOD IS DEMONSTRATED FROM IT

Thus far we have spoken of the quantity of blood passing through the heart and the lungs in the centre of the body, and in like manner from the arteries into the veins in the peripheral parts and the body at large We have yet to explain, however, in what manner the blood finds its way back to the heart from the extremities by the veins, and how and in ay these are the only vessels that convey the blood from the external to the central parts; which done, I conceive that the three fundamental propositions laid down for the circulation of the blood will be so plain, so well established, so obviously true, that theyposition will be made sufficiently clear from the valves which are found in the cavities of the veins thenisable by the senses

The celebrated Hieronymus Fabricius of Aquapendente, a most skilful anatomist, and venerable old man, or, as the learned Riolan will have it, Jacobus Silvius, first gave representations of the valves in the veins, which consist of raised or loose portions of the inner moid or semilunar shape They are situated at different distances from one another, and diversely in different individuals; they are connate at the sides of the veins; they are directed upwards towards the trunks of the veins; the two--for there are for the ard each other, mutually touch, and are so ready to co attempts to pass froreater vessels into the less, they coed, that the horns of those that succeed are opposite the middle of the convexity of those that and so on alternately

The discoverer of these valves did not rightly understand their use, nor have succeeding anatoe: for their office is by no means explained e are told that it is to hinder the blood, by its weight, froes of the valves in the jugular veins hang doards, and are so contrived that they prevent the blood fro upwards; the valves, in a word, do not invariably look upwards, but always toward the trunks of the veins, invariably towards the seat of the heart I, and indeed others, have soent veins, and in those of the es of which were directed towards the vena cava and vena portae Let it be added that there are no valves in the arteries, and that dogs, oxen, etc, have invariably valves at the divisions of their crural veins, in the veins that meet towards the top of the os sacrum, and in those branches which coravity from the erect position was to be apprehended Neither are there valves in the jugular veins for the purpose of guarding against apoplexy, as some have said; because in sleep the head is more apt to be influenced by the contents of the carotid arteries Neither are the valves present, in order that the blood may be retained in the divarications or smaller trunks and minuter branches, and not be suffered to flow entirely into the more open and capacious channels; for they occur where there are no divarications; although it must be owned that they are most frequent at the points where branches join Neither do they exist for the purpose of rendering the current of blood more slow from the centre of the body; for it seems likely that the blood would be disposed to floith sufficient slowness of its own accord, as it would have to pass fro separated fro from warmer into colder places

But the valves are solely reater into the lesser veins, and either rupture the 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 contraryescapes, or is less perfectly obstructed by the cornua of the one above, the fluid passing, as it were, by the chinks between the cornua, it is immediately received on the convexity of the one beneath, which is placed transversely with reference to the for any farther

And this I have frequently experienced in my dissections of the 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, on the contrary, it wasin the opposite direction, from without inwards, or from the branches towards the trunks and roots In many places two valves are so placed and fitted, that when raised they coether in the middle of the vein, and are there united by the contact of their ins; and so accurate is the adaptation, that neither by the eye nor by any otherthe line of contact be perceived But if the probe be now introduced from the extreates of a river, give way, and are ement plainly is to prevent all motion of the blood from the heart and vena cava, whether it be upwards towards the head, or doards towards the feet, or to either side towards the ar; in the larger and tending towards the smaller veins, is opposed and resisted by them; whilst the er branches is favoured, or, at all events, a free and open passage is left for it

But that this truth may be made the more apparent, let an ar 1) At intervals in the course of the veins, especially in labouring people and those whose veins are large, certain knots or elevations (B, C, D, E, F) will be perceived, and this not only at the places where a branch is received (E, F), but also where none enters (C, D): these knots or risings are all formed by valves, which thus show themselves externally And now if you press the blood fro 2,) and keep the point of a finger upon the vein inferiorly, you will see no influx of blood froer and the valve O will be obliterated; yet will the vessel continue sufficiently distended above the valve (O, G) The blood being thus pressed out and the vein eer of the other hand upon the distended part of the vein above the valve O, (fig

3,) and press doards, you will find that you cannot force the blood through or beyond the valve; but the greater effort you use, you will only see the portion of vein that is between the finger and the valve become more distended, that portion of the vein which is below the valve re 3)

It would therefore appear that the function of the valves in the veins is the samoid valves which we find at the commencement of the aorta and pulmonary artery, viz, to prevent all reflux of the blood that is passing over them

[NOTE--Woodcuts of the veins of the arures refer appear here in the original--C N B C]

Farther, the ar full and distended, if you press at one part in the course of a vein with the point of a finger (L, fig 4), and then with another finger streak the blood upwards beyond the next valve (N), you will perceive that this portion of the vein continues erade, precisely as we have already seen the case to be in fig 2; but the finger first applied (H, fig 2, L, fig 4), being removed, immediately the vein is filled fro 1 That the blood in the veins therefore proceeds fro in these vessels in this and not in the contrary direction, appears h in so with such perfect accuracy, or where there is but a single valve, do not seee of the blood froreater nus appear contrived ently, this is compensated either by the more frequent occurrence orvalves, or in some other way: the veins in short, as they are the free and open conduits of the blood returning TO the heart, so are they effectually prevented fro as its channels of distribution FROM the heart

But this other circu bound, and the veins id, and the valves proer over a vein in the situation of one of the valves in such a way as to co upwards froer of the other hand, streak the blood in the vein upwards till it has passed the next valve above (N, fig 4), the vessel now re removed for an instant, the vein is iain, and having in the saer below, and again the vessel becomes distended as before; and this repeat, say a thousand times, in a short space of time And now compute the quantity of blood which you have thus pressed up beyond the valve, and thenthe assumed quantity by one thousand, you will find that so h a certain portion of the vessel; and I do now believe that you will find yourself convinced of the circulation of the blood, and of its rapid motion But if in this experiment you say that a violence is done to nature, I do not doubt but that, if you proceed in the sath of vein as possible, and merely remark hat rapidity the blood floards, and fills the vessel from below, you will come to the same conclusion

CHAPTER XIV

CONCLUSION OF THE DEMONSTRATION OF THE CIRCULATION

And now I ive in brief my view of the circulation of the blood, and to propose it for general adoption

Since all things, both argument and ocular des, and heart by the force of the ventricles, and is sent for distribution to all parts of the body, where it makes its way into the veins and porosities of the flesh, and then flows by the veins from the circureater veins, and is by theht 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 reater than can be required for mere purposes of nutrition; 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; 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

CHAPTER XV

THE CIRCULATION OF THE BLOOD IS FURTHER CONFIRMED BY PROBABLE REASONS

It will not be foreign to the subject if I here show further, fros, that the circulation is matter both of convenience and necessity In the first place, since death is a corruption which takes place through deficiency of heat, [Footnote: Aristoteles De Respirations, lib ii et iii: De Part Anis are wars cold, there must be a particular seat and fountain, a kind of hoinal of the native fire, is stored and preserved; from which heat and life are dispensed to all parts as from a fountain head; from which sustenance may be derived; and upon which concoction and nutrition, and all vegetative energy may depend Now, that the heart is this place, that the heart is the principle of life, and that all passes in the manner just mentioned, I trust no one will deny

The blood, therefore, required to have ain to the heart; for sent to the external parts of the body far from its fountain, as Aristotle says, and withoutand keeping up heat and spirits under ail circu the thick or congealed by the cold of the extreme and outward parts, and robbed of its spirits, just as it is in the dead, it was iain receive heat and spirits, and all else requisite to its preservation--that, by returning, it should be renovated and restored