General Anatomy, Applied to Physiology and Medicine, Vol. 1 (of 3)

by Xavier Bichat

What part then have the arteries in the pulse? The following is what takes place in this great phenomenon; the arteries are always full of blood, the impulse that the blood in them receives from the left ventricle, is felt at the instant in the whole system, and even to its extremities. Imagine to yourself a syringe, the tube of which gives rise to an infinity of branches, which afterwards give origin successively to a number of smaller ones; if, when you push the piston of the syringe, its body and all the branches and smaller branches arising from it, are already full of fluid, it is evident that at the very instant in which the piston shall push the fluid in the body, it will go out on all sides through the open branches. Now suppose, that instead of a piston, you could make the parietes of the body of the syringe suddenly contract, the fluid at the instant of the contraction would spout out on all sides from these open branches. Another comparison will render this more evident; strike at one end of a long timber, the motion will be suddenly felt at the opposite one.

We can from this form an idea of what takes place at the instant of the contraction of the left ventricle. Authors have spoken of a wave or undulation of blood, being propagated through the whole arterial system, and formed by the two ounces of blood that are poured into the arteries at each contraction. The arterial motion should be thus considered, if the arteries were empty at the instant of contraction; but in their state of fulness, the impulse is generally and suddenly felt, and with almost as much force at the extremities as at the origin of the arteries; it is only in the ramifications that the motion becomes a little weakened. Fill with water the arteries of a dead body, and fix a syringe full at the aorta; at the instant you push the piston, the water will spout out of the tibial or any other artery, if you loosen an opening that had been previously made in them.

The idea that is commonly entertained of the progressive motion of the blood, is wholly incorrect. This fluid has been considered as flowing in the arteries almost like water in brooks. It is not so. At each contraction of the ventricle, it experiences suddenly a general motion that is felt at its extremities. Do you wish for another comparison? Suppose a syringe, to the tube of which is fitted a series of elastic pipes arising from each other; push the piston, you will see all these pipes swell simultaneously, become straight, and the fluid flow at the same time to the extremities, if they are open.

It is not the contraction of the arteries that drives the blood to their extremities. This is so true, that if you open one of these vessels at a distance from the heart, each jet that the blood will make in going out, will correspond to each contraction of the ventricle. Now if the arteries drove the blood to all the extremities, by contracting, their contraction and relaxation would alternate with those of the heart; but if it was so, each jet of the arterial throw should correspond to each relaxation of the ventricle; the contrary of this is the case as I have just said.

From this we see how very inaccurate is the common opinion, which I believed myself for many years, viz. that the auricles contract at the same time with the arteries, and the veins at the same time with the ventricles. The circulation of red blood is thus explained; 1st, the pulmonary veins drive the blood into the left auricle. 2d. This by contracting forces it into the ventricle, which dilates to receive it. 3d. This last contracts afterwards, sends it to the aorta which dilates at the instant of contraction; 4th, then this contracts to drive it to all the parts. This last does not take place; you can never observe it like the others, in a living animal. Examine as closely as possible, a great artery laid bare; it rises, but it does not dilate hardly at all in an ordinary state, nor does it contract. Contraction of the left ventricle; general motion of all the arterial blood; the entrance of this blood into the capillary system, are three things that take place at the same instant. It is like the blow on the timber, that is felt at one end, at the same time that it is received at the opposite.

We can form a very accurate idea of the circulation by examining the mesenteric arteries through the peritoneum, after having opened the abdomen of an animal; at each pulsation you see them all simultaneously rise and pulsate at their extremity as well as at their origin.

It is impossible to form an idea of the arterial motion, by considering the wave or undulation of blood as extending itself at each contraction in the arteries, and arriving afterwards successively at the extremities. Read all the authors upon the circulation; you will see that there is no subject that is treated oftener or more at length, than that of the course of the arterial blood, and yet there is no one in which you are left in more doubt and obscurity. Why? because all go upon a false principle, and all the consequences are inaccurate, where the principle itself is not correct.

It is not the wave of blood going from the ventricle, that is driven at each contraction into the capillary system; it is the portion of this fluid which is found nearest this system, as in the syringe, it is the portion that is in the tube that the piston forces out and not that with which it is in contact; whence it follows, that it is only at the end of some time that the blood arrives from the heart, at the general capillary system, that it remains during a number of contractions in the arteries, and that it is only successively expelled; which favours the mixture of the different principles that compose it.

From this manner of considering the arterial motion, which is the only real and admissible one, it is evidently impossible that the curves can injure this motion, besides this is proved by many facts.

I consider also as destitute of every kind of foundation all that has been said in the books of physiology, upon the causes of the delay occasioned in the course of the blood, 1st, by its passage from a narrower to a broader place, and by the conical form of the general arterial system; 2d, by friction; 3d, by the angles; 4th, by the anastomoses which give an opposite shock, &c. &c. All this would be true if the arteries were empty at the time of contraction, because the blood would then have in them, truly a progressive motion. But in the general and instantaneous impulse that the whole mass spread in the arterial system experiences, all these causes are evidently nothing. I return now to the trifling but very accurate comparison of the syringe. Suppose that a tube twisted in a thousand ways, with numerous angles, inequalities, internal projections, &c. was fixed to it; if the tube and the body of the syringe are full at the instant we push the piston, the water will escape suddenly from the extremity of this tube with as much force as if it was straight and short. It is so true that all the causes of delay, which would have some effect, if the arteries were empty at the instant the blood is driven into them, have none in their ordinary state, that many judicious observers, who even admitted the delay, have seen in their experiments that the motion was every where the same, in the smaller branches as in the trunks. Why did not this undeceive them? We know that the pulse is the same in all parts of the arterial system; how could it be if there was this delay? What has greatly retarded the progress of the physiology of the circulation, is the idea that is attached to the velocity of the course of the red blood. This velocity cannot be rightly estimated, because the motion is not successive, because, to speak correctly, the blood does not flow; it is suddenly driven by a general impulse, in which we cannot calculate any thing.