Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/111

Rh 95 VASCULAR SYSTEM THE term vascular system designates all tlie arrange ments in the body connected with the circulation of the blood. A description of the anatomy of the various organs as found in man is given under ANATOMY (vol. i. p. 899 sq. and an account of various modifications of the circulatory apparatus under the headings designating the great groups of the animal kingdom, such as MOLLUSCA, CRUSTACEA, ICHTHYOLOGY, AMPHIBIA, REPTILES, BIRDS ; and reference may be made to the articles NUTRITION and RESPIRATION for details as to the formation, physical and chemical properties, and functions of the blood. The present article is devoted to a consideration of the mechan ism by which the circulation is carried on in the Mammalia and in man, a branch of physiology which has been more successfully investigated than any other department of the science. HISTORICAL SKETCH. Galen, following Erasistratus and Aristotle, clearly dis- .nguished arteries from veins, and was the first to over throw the old theory of Erasistratus that the arteries con tained air. According to him, the vein arose from the liver in two great trunks, the vena porta and vena cava. The first was formed by the union of all the abdominal veins, which absorbed the chyle prepared in the stomach and intestines, and carried it to the liver, where it was con verted into blood. The vena cava arose in the liver, divided into two branches, one ascending through the dia phragm to the heart, furnishing the proper veins of this organ ; there it received the vena azygos, and entered the right ventricle, along with a large trunk from the lungs, evidently the pulmonary artery. The vena azygos was the superior vena cava, the great vein which carries the venous blood from the head and upper extremities into the right auricle. The descending branch of the great trunk supposed to originate in the liver was the inferior vena cava, below the junction of the hepatic vein. The arteries arose from the left side of the heart by two trunks, one having thin walls, the pulmonary veins, the other having thick walls, the aorta. The first was supposed to carry blood to the lungs, and the second to carry blood to the body. The heart consisted of two ventricles, communicating by pores in the septum ; the lungs were parenchymatous organs communicating with the heart by the pulmonary veins. The blood-making organ, the liver, separates from the blood subtle vapours, the natural spirits, which, carried to the heart, mix with the air introduced by respiration, and thus form the vital sj)irits ; these, in turn carried to the brain, are elaborated into animal spirits, which are distributed to all parts of the body by the nerves. 1 Such were the views of Galen, taught until early in the 16th century. Jacobus Berengarius of Carpi (ob. 1527) investigated the structure of the valves of the heart. Andreas Vesale . or Vesalius (1514-1564) contributed largely to anatomical knowledge, especially to the anatomy of the circulatory organs. He determined the position of the heart in the chest ; he studied its structure, pointing out the fibrous rings at the bases of the ventricles ; he showed that its wall consists of layers of fibres connected with the fibrous rings ; and he described these layers as being of three kinds, straight or vertical, oblique, and circular or trans verse. From the disposition of the fibres he reasoned as to the mechanism of the contraction and relaxation of the heart. He supposed that the relaxation, or diastole, was 1 See Burggraeve s Ifistoire de V Anatomic, Paris, 1880, in which he refers to many of the older authors, also to the articles GALKN and ANATOMY. accounted for principally by the longitudinal fibres con tracting so as to draw the apex towards the base, and thus cause the sides to bulge out ; whilst the contraction, or systole, was due to contraction of the transverse or oblique fibres. He showed that the pores of Galen, in the septum between the ventricles, did not exist, so that there could be no communication between the right and left sides of the heart, except by the pulmonary circulation. He also investigated minutely the internal structure of the heart, describing the valves, the columnx carnex, and the musculi papillares. He described the mechanism of the valve.s with much accuracy. He had, however, no conception either of a systemic or of a pulmonary circulation. To him the heart was a reservoir from which the blood ebbed and flowed, and there were two kinds of blood, arterial and venous, having different circulations and serving dif ferent purposes in the body. Vesalius was not only a great anatomist : he was a great teacher ; and his pupils carried on the work in the spirit of their master. Promi nent among them was Gabriel Fallopius (1523-1562), who studied the anastomoses of the blood-vessels, without the art of injection, which was invented by Frederick Ruysch (1638-1731) more than a century later. Another pupil was Columbus (Matthieu Reald Columbo, ob. 1559), first O oium- a prosector in the anatomical rooms of Vesalius and after- k&quot; 8 - wards his successor in the chair of anatomy in Padua ; his name has been mentioned as that of one who anticipated Harvey in the discovery of the circulation of the blood. A study of his writings clearly shows that he had no true knowledge of the circulation, but only a glimpse of how the blood passed from the right to the left side of the heart. In his work there is evidently a sketch of the pulmonary circulation, although it is clear that he did not understand the mechanism of the valves, as Vesalius did. As regards the systemic circulation, there is the notion simply of an oscillation of the blood from the heart to the body and from the body to the heart. Further, he upholds the view of Galen, that all the veins originate in the liver ; and he even denies the muscular structure of the heart. 2 In 1553 Michael Servetus (1511-1553), a pupil or junior Servetus. fellow-stxident of Vesalius, in his Christianismi Restitutio, described accurately the pulmonary circulation. 3 Servetus perceived the course of the circulation from the right to the left side of the heart through the lungs, and he also recognized that the change from venous into arterial blood took place in the lungs and not in the left ventricle. Not so much the recognition of the pulmonary circulation, as that had been made previously by Columbus, but the dis covery of the respiratory changes in the lungs constitutes Servetus s claim to be a pioneer in physiological science. Andrea Cesalpino (1519-1603), a great naturalist of this rvsal- period, also made important contributions towards the di.s- i&quot;&quot;- covery of the circulation, and in Italy he is regarded as the real discoverer. 4 Cesalpinus knew the pulmonary circulation. Further, he was the first to use the term 2 An interesting account of the views of the precursors of Harvey will be found in Willis s edition of the Works of Harvey, published by the Sydenham Society. Conip. also P. Flourens, Jli-stvire de la De- couverte de la Circulation du Samj (Paris, 1854), and Prof. R. Owen, Experimental Physiology, its Benefits to Mankind, with an Address on Unveiling the Statue of W. Harvey, at Folkestone, 6th August 1SSI. 3 The passage is quoted under ANATOMY, vol. i. p. 810 n. ; comp. also HARVEY. See Willis, Serve tu-s and Calvin, London, 1877. 4 A learned and critical series of articles by Sampson Gamgee in the Lancet, in 1876, gives an excellent account of the controversy as to whether Cesalpinus or Harvey was the true discoverer of the circula tion ; see also the Harveian oration for 1882 by George Johnston (Lancet, July 1882), and Prof. G. M. Humphry, Journ. Anat. and Phys., October 1882.