30 CIRCULATION OF THE BLOOD. 



two great blood-vessels, the vena cava and aorta, arising from the heart, and 

 that the aorta and its branches carry blood. Galen, however, demonstrated 

 experimentally the presence of blood in the arteries, by including a portion 

 of one of these vessels between two ligatures, in a living animal ; but his 

 ideas of the communication' between the arteries and veins were erroneous, 

 for he believed in the existence .of small orifices in the septum between the 

 ventricles of the heart, a mistake that was corrected by Vesalius, at about 

 the middle of the sixteenth century. 



In 1553, Michael Servetus, who is generally regarded as the discoverer of 

 the passage of the blood through the lungs, or the pulmonary circulation, 

 described in a work on theology the course of the blood through the lungs, 

 from the right to the left side of the heart. This description, complete as 

 it is, was merely incidental to the development of a theory with regard to 

 the formation of the soul and the development of what were called animal 

 and vital spirits (spiritus). 



A few years later, Colombo, professor of anatomy at Padua, and Cesal- 

 pinus, of Pisa, described the passage of the blood through the lungs, though 

 probably without any knowledge of what had been written by Servetus. To 

 Cesalpinus is attributed the first use of the expression circulation of the 

 blood ; and he also remarked that after ligature or compression of veins, the 

 swelling is always below the point of obstruction. 



The history of the discovery of the valves in the veins is quite obscure, 

 although priority of observation is almost universally conceded to Fabricius. 

 As regards this point, only the dates of published memoirs are to be con- 

 sidered, notwithstanding the assertion of Fabricius that he had seen the 

 valves in 1574. In 1545, Etienne described, in branches of the portal vein, 

 " valves, which he called apophyses, and which he compared to the valves of 

 the heart." In 1551, Amatus Lusitanus published a letter from Cannanus, 

 in which it is stated that he had found valves in certain of the veins. In 

 1563, Eustachius published an account of the valves of the coronary vein. 

 In 1586, a clear account, by Piccolhominus, of the valves of the veins was 

 published. Fabricius gave the most accurate descriptions and delineations 

 of the valves, and his first publication is said to have appeared in 1603. He 

 demonstrated the valves to Harvey, at Padua ; and it is probable that this 

 was the origin of the first speculations by Harvey on the mechanism of the 

 circulation. 



In the work of Harvey are described, first the movements of the heart, 

 which he exposed and studied in living animals. He described minutely all 

 the phenomena which accompany its action ; its diastole, when it is filled 

 with blood, and its systole, when the fibres of which the ventricles are com- 

 posed contract simultaneously, and "by an admirable adjustment all the 

 internal surfaces are drawn together, as if with cords, and so is the charge of 

 blood expelled with force." From the description of the action of the 

 ventricles, he passed to the auricles, and showed how these, by their con- 

 traction, filled the ventricles with blood. By experiments upon serpents and 

 fishes, he proved that the blood fills the heart from the veins and is sent out 



