158 HISTORICAL RETROSPECT OF THE CIRCULATION. 



completely separate auricles and two separate ventricles. In the halicore the apex of the ven- 

 tricles is deeply cleft. Some animals have accessory hearts, e.g., the eel in its caudal vein. 

 They are very probably lymph-hearts {Robin). The veins of the wing of the bat pulsate (Schiff). 

 The lowest vertebrate, amphioxus, has no heart, but only a rhythmically-pulsating vessel. 



Amongst blood-glands, the thymus and spleen occur throughout the vertebrata, the latter 

 being absent only in amphioxus and a few fishes. 



Amougst invertebrata a closed vascular system, with pulsatile movement, occurs here and 

 there, e.g., amongst ecbinodermata (star-fishes, sea-urchins, holothurians) and the higher worms. 

 The insects have a pulsating "dorsal vessel" as the central organ of the circulation, which 

 is a contractile tube provided with valves and dilated by muscular action ; the blood being 

 propelled rhythmically in one direction into the spaces which lie amongst the tissues and organs, 

 so tnat these animals do not possess a closed vascular system. The mollusca have a heart with 

 a lacunar vascular system. The cephalopods (cuttle-fish) have three hearts a simple arterial 

 heart, and two venous simple gill-hearts, each placed at the base of the gills. The vessels form 

 a completely closed circuit. The lowest animals have either a pulsatile vesicle, which propels 

 the colourless juice into the tissues (infusoria), or the vascular apparatus may be entirely 

 absent. 



105- HISTORICAL RETROSPECT. The ancients held various theories regarding the 

 movement of the blood, but they knew nothing of its circulation. According to Aristotle 

 (384 B.C.), the heart, the acropolis of the body, prepared in its cavities the blood, which 

 streamed through the arteries as a nutrient fluid to all parts of the body, but never returned 

 to the heart. With Herophilus and Erasistratus (300 B.C.), the celebrated physicians of the 

 Alexandrian school, originated the erroneous view that the arteries contain air, which was 

 supplied to them by the respiration (hence the name artery). They were led to adopt this 

 view from the empty condition of the arteries after death. By experiments upon animals, 

 Galen disproved this view (131-201 a.d.) "Whenever I injured an artery," he says, " blood 

 always flowed from the wounded vessel. On tying part of an artery between two ligatures, the 

 }>art of the artery so included is always filled with blood." 



Still, the idea of a single centrifugal movement of the blood was retained, and it was assumed 

 that the right and left sides of the heart communicated directly by means of openings in 

 the septum of the heart, until Vesalius showed that there are no openings in the septum. Michael 

 Servetus (a Spanish monk, burned at Geneva, at Calvin's instigation, in 1553) discovered 

 the pulmonary circulation. Cesalpinus confirmed this observation, and named it " Circulatio. " 

 Fabricius ab Aquapendente (Padua, 1574) investigated the valves in the veins more carefully 

 (although they were known in the 5th century to Theodoretus, Bishop in Syria), and he was 

 acquainted with the centripetal movement of the blood in the veins. Up to this time it was 

 imagined that the veins carried blood from the centre to the periphery, although Vesalius 

 was acquainted with the centripetal direction of the blood-stream in the large venous trunks. 

 At length William Harvey, who was a pupil of Fabricius (1604), demonstrated the complete 

 circulation (1616-1619), and published his great discovery in 1628. [For the history of the 

 discovery of the circulation of the blood, see the works of Willis on " W. Harvey," " Servetus 

 and Calvin," those of Kirchner, and the various Harveian orations.] 



According to Hippocrates, the heart is the origin of all the vessels ; he was acquainted with 

 the large vessels arising from the heart, the valves, the chordae teudineae, the auricles, and the 

 closure of the semi-lunar valves. Aristotle was the first to apply the terms aorta and venae 

 cavse ; the school of Erasistratus used the term carotid, and indicated the functions of the 

 venous valves. In Cicero a distinction is drawn between arteries and veins. Celsus mentions 

 that if a vein be struck below the spot where a ligature has been applied to a limb, it bleeds, 

 while Aretaeus (50 a.d.) knew that arterial blood was bright and venous dark. Pliny (t 79 

 A.D.) described the pulsating fontanelle in the child. Galen (131-203 a.d.) was acquainted 

 with the existence of a bone in the septum of the heart of large animals (ox, deer, elephant). 

 He also surmised that the veins communicated with the arteries by fine tubes. The demon- 

 stration of the capillaries, however, was only possible by the use of the microscope, and 

 employing this instrument, Malpighi (1661) was the first to demonstrate the capillary circula- 

 tion. Leuwenhoek (1674) described the capillary circulation more carefully, as it may be seen 

 in the web of the frog's foot and other transparent membranes. Blancard (1676) proved the 

 existence of capillary passages by means of injections. William Cooper (1697) proved that the 

 same condition exists in warm-blooded animals, and Ruysch made similar injections. Stenson 

 (born 1638) established the muscular nature of the heart, although the Hippocratic and 

 Alexandrian schools had already surmised the fact. Cole proved that the sectional area of the 

 blood-stream became wider towards the capillaries (1681). Joh. Alfons Borelli (1608-1679) was 

 the first to estimate the amount of work done by the heart. 



