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 lesser to the greater veins, and is by them finally discharged into the vena cava 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 ingestor, and is
much greater than can be required for mere pur ses of nutrition, it is absolutely necessary to conclude that the bfdgd 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 " (bk. x. ch. xiv. p. 68).
Opposed to Caspar Hofmann of Nuremberg (1571-1623), Veslingius (Vesling) of Padua (1598-1649), and J. Riolanus the younger, this new theory was supported by Roger Drake, a young Englishman, who chose it for the subject of a. graduation thesis at Leiden in 1637, by Werner Rolfinck of Jena (1599-1673), and especially by Descartes, and quickly gained the ascendant; and its author had the satisfaction of seeing it confirmed by the discovery of the capillary circulation, and unig, versally adopted. The circulation in the capillaries vlrvvld- between the arteries and the veins was discovered by Marcellus Malpighi (1628-1694) of Bologna in 1661.[1] He saw it first in the lungs and the mesentery of a frog, and the discovery was announced in the second of two letters, Epistola de Pulmonibus, addressed to Borelli, and dated 166I.1 Malpighi actually showed the capillary circulation to the astonished eyes of Harvey. Anthony van Leeuwenhoek (1632-1723) in 1673 repeated Malpighi's observations, and studied the capillary circulation in a bat's wing, the tail of a tadpole and the tail of a fish. William Molyneux studied the circulation in the lungs of a water newt in 1683.[2]
The idea that the same blood was propelled through the body in a circuit suggested that life might be sustained by renewing the blood in the event of some of it being lost. About 1660 Lower, a London physician (died 1691), succeeded in transferring the blood of one animal directly from its blood vessels into those of another animal. This was first done by passing a “ quill” or a “ small crooked pipe of silver or brass ” from the carotid artery of one dog to the jugular vein of another.[3] This experiment was repeated and modified by Sir Edmund King (1629-1709), Thomas Coxe (1615-1685), Gayant and Denys with -such success as to warrant the operation being performed on man, and accordingly it was carried out by Lower and King on the 23rd of November 1667, when blood from the arteries of a sheep was directly introduced into the veins of a man.[4] It would appear that the operation had previously been performed with success in Paris.
The doctrine of the circulation being accepted, physiologists next directed their attention to the force of the heart, the Fame 0, pressure of the blood in the vessels, its velocity, heart and and the phenomena of the pulse wave. Giovanni Alphonso Borelli (1608-1679) investigated the circulation during the lifetime of Harvey. He early conceived the design of applying mathematical principles to the explanation of animal functions; and, although he fell into many errors, he must be regarded as the founder of animal mechanics. In his De Motu Anirnaliurn (1680-85) he stated his theory of the circulation in eighty propositions, and in prop. lxxiii., founding on a supposed relation between the bulk and the strength of muscular fibre as found in the ventricles, erroneously concluded that the force of the heart was equal to the pressure of a weight of 180,000 lb. He also recognized and figured the spiral arrangement of fibres in the ventricles. The question was further investigated by James Kem Keill, a Scottish physician (1673-1719), who in his Account of Animal Secretion, the Quantity of Blood in the Human Body, and Muscular Motion (1708) attempted to estimate the velocity of blood in the aorta, and gave it at 52' ft. per minute. Then, 'allowing for the resistance of the vessels, he showed that the velocity diminishes towards the smaller vessels, and arrived at the amazing conclusion that in the smallest vessels it travels at the rate of i in. in 278 days, good example of the extravagant errors made by the mathematical physiologists of the period. Keill further described the hydraulic phenomena of the circulation in papers communicated to the Royal Society and collected in his Essays on Several Parts of the Animal Oeconomy (1717). In these essays, by estimating the quantity of blood thrown out of the heart by each contraction, and the diameter of the aortic orifice, he calculated the velocity of the blood. He stated (pp. 84, 87) that the blood sent into the aorta with each contraction would form a cylinder 8 in. (2 oz.) in length and be driven along with a Velocity of 156 'ft. per minute. Estimating then the resistances to be overcome in the vessels, he found the force of the heart to be “little above 16 oz., ” -a remarkable difference from the computation of Borelli. Keill's method was ingenious, and is of historical interest as being the first attempt to obtain quantitative results; but it failed to obtain true results, because the data on which he based his calculations were inaccurate. These calculations attracted the attention not only of the anatomic-physiologists, such as Haller, but also of some of the physicists of the time, notably of ]urin and D. Bernoulli. Iurin (died 1750) gave the force of the left ventricle at 9 lb 1 oz., and that of the right ventricle at 6 lb 3 oz. He also stated with remarkable clearness, considering that he reasoned on the subject as a physicist, without depending on experimental data gathered by himself, the influence on the pulse induced by variations in the power of the heart or in the resistance to be overcome.[5] The experimental investigation of the problem was supplied Ha, ” by Stephen Hales (1677-1761), rector of Teddington in ° Middlesex, who in 1708 devised the method of estimating the force of the heart by inserting a tube into a large artery and observing the height to which the blood was impelled into' it. Hales is the true founder of the modern experimental method in physiology. He observed in a horse that the blood rose in the vertical tube, which he had connected with the crural artery, to the height of 8 ft. 3 in. perpendicular above the level of the left ventricle of the heart. But it did not attain its full height at once: it rushed up about half-way in an instant, and afterwards gradually at each pulse 12, 8, 6, 4, 2, and sometimes. 1 in. When it was at its full height, it would rise and fall at and after each pulse 2, 3 or 4 in.; and sometimes it would fall 12 or 14 in., and have there for a time the same vibrations up and down at and after each pulse as it had when it was at its full height, to which it would rise again after forty or fifty pulses.[6] He then estimated the capacity of the left ventricle by a method of employing waxen casts, and, after many such experiments and measurements in the horse, ox, sheep, fallow deer and dog, , he calculated that the force of the left ventricle in man is about equal to that of a- column of blood 7% ft. high, weighing 51% lb, or, in other words, that the pressure the left ventricle has to overcome is equal to the pressure of that weight. When we contrast the enormous estimate of Borelli (180,000 lb) with the under-estimate of Keill (16 oz.), and when we know that the estimate of Stephen Hales (1677-1761), as corroborated by recent investigations by means of elaborate scientific appliances, isvery near the truth, we recognize the far higher service rendered to science by careful and judicious experiment than by speculations, however ingenious. With the exception of some calculations, by Dan Bernoulli (1700-1782) in 1748, there was no great contribution to haemadynamics till 1808, when two remarkable papers appeared from Thomas Young. (1773-1829). In the first, entitled “Hydraulic Investigations,” which appeared in the Phil. Trans., he investigated the friction and discharge of fluids running in pipes and the velocity of rivers, the
- ↑ See his Opera Omnia, vol. i. p. 328.
- ↑ Lowthorp, Abridgement of Trans. Roy. Soc., 5th ed. vol. iii. p. 230.
- ↑ Ibid. p. 231.
- ↑ Ibid. p. 226.
- ↑ Jones, Abridgement of Phil. Trans. (3d ed., 1749), vol. v. p. 223. See also for an account of the criticisms of D. Bernoulli the elder and others, Halle;-'s Elementa Physiologiae, vol. i. p. 448.
- ↑ Hales, Statical Essays, containing Haemastatics, &c. (1733), vol. ii. p. 1.
