In other words, that

Fig. 297.

would therefore, be forty pounds; but this is, of course, a rude approximation. In such a deranging experiment, the force of the heart cannot fail to be modified; and it is so much affected by age, sex, temperament, idiosyncrasy, &c., that the attainment of accurate knowledge on the subject is impracticable. The indefinite character of our information on this matter is indeed sufficiently shown by the investigations of M. Poiseuille, which led him to suppose, that the force with which the organ propels the blood into the human aorta is about 4 pounds, 3 ounces, and 43 grains, and if Valentin's estimate of the muscular force of the right ventricle being one-half that of the left be taken, it must propel the blood into the lungs with a force only equal to about two pounds, two ounces. By means of an instrument, which, from its use, he terms hæmadynamometer, M. Poiseuille has endeavoured to show, that the blood is urged forward with as great a momentum in a small artery, far from the heart, as in any important branch near it. there is a uniform amount of pressure exerted by the blood upon the coats of the arteries in every part of the body;-those in the immediate vicinity of the heart being distended by an equal force with those most remote from it. M. Poiseuille3 made the experiment on the carotid, and muscular branch of the thigh of the horse, and notwithstanding the very great dissimilarity in the diameter of the two tubes, and in their distance from the heart, the displacement of the mercury was exactly the same in both. This inference, if correct, -and the experiments have been repeated by M. Magendie and others with corresponding results, is important in a therapeutical point of view, as it leads to the belief, that if it be desirable to lessen the quantity of the circulating fluid, it is of little consequence what vessel is opened. The hæmadynamometer employed by M. Poiseuille, consists of a bent glass tube, of the form represented in the marginal figure, filled with mercury in the lower bent part, a, d, e. The horizontal part b, provided with a brass head, is fitted into the artery, and a small quantity of a solution of carbonate of soda is interposed between the mercury and the blood, which is allowed to enter the tube with the view of preventing coagulation. When the blood is allowed to press upon the fluid in the horizontal limb, the rise of the mercury

Hæmadynamometer.

1 Arnott's Elements of Physics, Amer. edit., pp. 447 and 461, Philad., 1841.

2 Magendie's Journal de Physiologie, x. 241.

Ibid., ix. 46.

Leçons sur le Sang, &c., or translation in Lond. Lancet, Sept. 1838 to March, 1839; and in Bell's Select Medical Library, p. 57, Philad., 1839.

towards e, measured from the level to which it has fallen towards d, gives the pressure under which the blood moves.

Estimates by Valentin' as to the force of the heart make it even less than those of M. Poiseuille. He states, that in man and the higher mammalia, the absolute force exerted by the left ventricle is equal to th of the weight of the body; and that by the right ventricle equal toth of the same.

During the diastole of the ventricles, the pressure, as indicated by the instrument, is somewhat diminished. It was observed by Hales,2 that the column of blood in a tube inserted into an artery fell after each pulsation. The pressure must obviously be augmented or diminished by anything that adds to or detracts from the heart's action; and it will be seen afterwards, that it is materially modified by the respiratory movements.3

b. Circulation in the Arteries.

The blood, propelled from the heart by the series of actions we have described, enters the two great blood vessels; the pulmonary artery from the right ventricle, and the aorta from the left; the former of which sends it to the lungs, the latter to every part of the system; and, in both vessels, it is prevented from returning into the corresponding ventricles by the depression of the semilunar valves. We have now to inquire into the circumstances, that act upon it in the arteries, and whether it be the contraction of the ventricle, which is alone concerned in its progression.

Harvey and all the mechanical physiologists regarded the arteries as entirely passive in the circulation, and as acting like so many lifeless tubes; the heart being, in their view, the sole agent. We have, however, numerous reasons for believing that the arteries are concerned to a certain degree in the progression of the blood. If we open a large artery in a living animal, the blood flows in distinct pulses; but this effect gradually diminishes as the artery recedes from the heart, and ultimately ceases in the smallest ramifications:-seeming to show, that the force, exerted by the heart, is not the only one concerned. It is manifest, too, that if such was the case, the blood ought to flow out of the aperture, when the artery is opened, at intervals coinciding with the contractions of the organ; and that during the diastole of the artery no blood ought to issue. This, however, is not the case, notwithstanding the authority of Bichat and some others is in its favour. The flow is uninterrupted; but in jets or pulses, coinciding with the contractions of the ventricles. Again, if two ligatures be put round an arterial trunk, at some distance from each other, and a puncture be made between the ligatures, the blood flows with a jet,-indicating that compression is exerted upon it; and if the diameter of the artery be measured with a pair of compasses, before and after puncturing the vessel, it will be found manifestly smaller in the latter case;-an ex

1 Lehrbuch der Physiologie des Menschen, i. 415, Braunschweig, 1844.

2 Op. cit., ii. 2.

3 Ludwig, in Müller's Archiv. für Anatomie, u. s. w., Heft iv. s. 242, Berlin, 1847.

◄ Exercitatio Anat. De Motu Cordis et Sanguinis, &c., Rotterd., 1648.

periment which shows the fallacy of a remark of Bichat,-that the force with which the arteries return upon themselves is insufficient to expel the blood they contain. An experiment of M. Magendie1 exhibits this more clearly. He exposed the crural artery and vein in a dog, and passed a ligature behind the vessels, tying it strongly at the posterior part of the thigh, so that the blood could only pass to the limb by the artery, and return by the vein. He then measured, with a pair of compasses, the diameter of the artery; and on pressing the vessel between his fingers, to intercept the course of blood, it was observed to diminish perceptibly in size below the part compressed, and to empty itself of its blood. On readmitting the blood, by removing the fingers, the artery became gradually distended at each contraction of the heart, and resumed its previous dimensions.

These facts prove, that the arteries contract; but the kind of contraction has given occasion to discussion. Under the idea that their middle coat is muscular, it was conceived formerly, that they exert a similar action on the blood to that of the heart; dilating to receive it from that organ, and contracting to propel it forwards;-their systole being synchronous with that of the auricles and the diastole of the ventricles, and their diastole with that of the auricles and the systole of the ventricles. The principal reasons urged in favour of this view are; the fact of the circulation being effected solely by the arteries in acardiac fœtuses, and in animals that have no heart;-the assertion of MM. Lamure and Lafosse, that they noticed, in an experiment on the carotid artery, similar to that described above, that the vessel continued to beat between the ligatures;—the affirmations of Verschuir, Bikker, Giulio, and Rossi,3 Thomson, Parry,' Hastings, Wedemeyer, and numerous others, that when they irritated arteries with the point of a scalpel, or subjected them to the electrical and galvanic influences, they exhibited manifest contractility; and lastly, the fact, that the pulse is not perfectly synchronous in different parts of the body, which ought to be the case, were the arteries not possessed of distinct

action.

4

2

The chief objection to the views founded on the muscularity of the middle coat was the want of evidence of the fact. In the anatomical proem to the function of the circulation it was stated, that this coat had not seemed to anatomists to consist of fibrous or muscular tissue; and that the experiments of MM. Magendie, Nysten, and others, had not been able to exhibit any contraction, on the application to it of the ordinary excitants of muscular irritability. The chemical analyses of Berzelius' and Young also appeared to show, that the transverse fibres differ essentially from those of proper muscles. It has been suggested, however, that the older analyses may have been made on the largest

1 Journal de Physiologie, i. 111; and Précis, &c., ii. 386.

2 De Arteriar. et Venar. Vi Irritabili, &c., Gröning., 1766.

* Elémens de Médec. Opérat., Turin, 1806.

4 Lectures on Inflammation, p. 83, Edinb., 1813; also, 2d Amer. edit., Philad., 1831.

5 On the Arterial Pulse, p. 52, Bath, 1816.

On Inflammation of the Mucous Membrane of the Lungs, p. 20, Lond., 1820.

View of the Progress of Animal Chemistry, p. 25, Lond., 1813.

An Introduction to Medical Literature, p. 501, Lond., 1813.

arteries in which muscular fibres scarcely exist;' for histologists-as elsewhere shown-are now agreed, that, in the smaller arteries, more especially, the middle coat is partly composed of nonstriated or unstriped muscular tissue. Moreover, if any doubt existed in regard to the contractile action of the smaller arteries, it ought to be removed by the experiments of MM. E. and E. H. Weber, accurate observers, which were made with the rotating magneto-electric apparatus upon the arteries of the mesentery of frogs between 4th and 14th of a Paris line in diameter. When vessels between these dimensions were exposed to the electric stream they did not immediately respond to the irritation; but in a few seconds they began to contract, so that in from five to ten seconds their diameter was diminished one-third. If the stimulus was ́continued, the diminution of size went on until the diameter was reduced to one-third or even one-sixth of what it was originally, so that only a single row of blood corpuscles could pass along the vessel, and at last became completely closed unless the stimulus was removed. They found, however, no change produced in the capillaries when the magneto-electric current was applied to them; but it appeared to cause an unusual adhesion of the corpuscles to each other, and to the parietes of the vessels, and a consequent stagnation of the circulating fluid in them. Nor did the larger arteries exhibit any signs of contraction when the stream was directed to them.

If an artery be exposed in a living animal, we observe none of that contraction and dilatation which is perceptible in the heart; although a manifest pulsation is communicated to the finger placed over it. The phenomena of the pulse will engage attention speedily. We may merely remark, at present, that the pulsations are manifestly more dependent upon the action of the heart than upon that of the arteries. In syncope, they entirely cease; and whilst they continue beneath an aneurismal tumour, because the continuity of the vessel is not destroyed, they completely cease beneath a ligature so applied around an artery as to cut off the flow of blood. Bichat attached an inert tube to the carotid artery of a living animal, so that the blood could flow through it: the same kind of pulsation was observed in it as in the artery. To this he adapted a bag of gummed taffeta, so as to simulate an aneurismal tumour: the pulsations were evidenced in the bag. If, again, arterial blood be passed into a vein, the latter vessel, which has ordinarily no pulsation, begins to beat; whilst, if blood from a vein be directed into an artery, the latter ceases to beat.3 Another class of physiologists have reduced the whole of the arterial action to simple elasticity; a property, which the yellow tissue that composes the proper membrane of the artery seems to possess in an unusual degree. Such is the opinion of M. Magendie. "Admitting it to be certain," he remarks, "that contraction and dilatation occur in arteries, I am far from thinking, with some authors of the last century,

1 Kirkes and Paget, Manual of Physiology, p. 91, Amer. edit., Philad., 1849.

2 Müller's Archiv. für Anatomie, u. s. w., H. ii. s. 282, Jahrgang, 1847.

3 Adelon, art. Circulation, in Dict. de Médecine, lère édit., v. 321, Paris, 1822, and Physiol. de l'Homme, edit. cit., iii. 380.

Précis, &c., edit. cit., ii. 387

Fig. 298.

C

that they dilate of themselves, and contract in the manner of muscular fibres. On the contrary, I am certain, that they are passive in both cases, that is, that their dilatation and contraction are the simple effect of the elasticity of their parietes, put in action by the blood, which the heart sends incessantly into their cavity," and he farther remarks, that there is no difference, in this respect, between the large and small arteries. As regards the larger arteries, it is probable that this elasticity is the principal but not the only action exerted; and that it is the cause why the blood flows in a continuous, though pulsatory, stream, when an opening is made into them; thus acting like the reservoir of air in certain pumps. In the pump A B, represented in the marginal figure, were there no air-vessel C, the water would flow through the pipe E at each stroke of the piston, but the stream would be interrupted. By means of the air-vessel this is remedied. The water, at each stroke, is sent into the vessel; the air contained in the air-vessel is thus compressed, and its elasticity thereby augmented; so that it keeps up a constant pressure on the surface of the water, and forces it out of the vessel through the pipe D in a nearly uniform stream.Now, in the heart, the contraction of the ventricle acts like the depression of the piston; the blood is propelled into the artery in an interrupted manner, but the elasticity of the bloodvessel presses upon the blood, in the same manner as the air in the air-vessel presses upon the water within it; and the blood flows along the vessel in an uninterrupted, although pulsatory, stream. There are many difficulties, however, in the way of admitting the whole of the action of the arteries in the circulation to be dependent upon simple elasticity. The heart of a salamander was opened by Spallanzani;1 the blood continued to flow through the vessels for twelve minutes after the operation. The heart of a tadpole was cut out; the circulation was maintained for some time in several of the vascular ramifications of the tail. The heart of the chick in ovo was destroyed immediately after contraction; the arterial blood took a retrograde direction, and the momentum of the venous blood was redoubled. The circulation continued in this manner for eighteen minutes. Dr. Wilson Philip2 states, that he distinctly saw the circulation in the smaller vessels, for some time after the heart had been removed from the body, and a similar observation was made by Dr. Hastings.3 The latter gentleman states, that in the large arterial trunks, and even in the veins, he has

Experiments on the Circulation, &c., translated by R. Hall, Lond., 1801.

2 An Experimental Inquiry into the Laws of the Vital Functions, Lond., 1817; and Lond. Med. Gazette, for March 25th, 1837, p. 952. 3 Op. citat., p. 51.