DISCOVERY OF THE CIRCULATION. 173 



means of vivisections. As is evident when we consider the 

 state of science at that time, anatomists had long been 

 preparing the way for the discovery of the circulation, though 

 they knew little of the functions of the parts they described. 

 The conformation of the heart and vessels, and even the 

 arrangement of the valves of the veins, did not lead them to 

 suspect the course of the blood ; but a few well conceived 

 experiments on living animals have made it appear so sim- 

 ple, that we now wonder it remained unknown so long. 

 Furthermore, these experiments made it evident that there 

 was a communication at the periphery between the arteries 

 and the veins. 



In the work of Harvey are described, first, the move- 

 ments of the heart, which he exposed and studied in living 

 animals. He describes 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 composed 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 passes to the auricles, and shows how these, by their con- 

 traction, fill 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 into the arteries. Ex- 

 posing the heart and great vessels in these animals, he applied 

 a ligature to the veins, which had the effect of cutting off 

 the supply from the heart so that it became pale arid flaccid ; 

 and by removing the ligature the blood could be seen flowing 

 into the organ. "When, on the contrary, a ligature was 

 applied to the artery, the heart became unusually distended, 

 which continued as long as the obstruction remained. "When 

 the ligature was removed, the heart soon returned to its 

 normal condition. 1 



The descriptions given by Harvey were the result of nu- 



1 The Works of William Harvey, M. D. Sydenham Edition, p. 63. 



