THE CIRCULATION OF THE BLOOD. 439 



it, he conceived the idea of making experiments, in 

 order to determine what is the course of the blood 

 in its vessels. He found that when he tied up 

 veins in various animals, they swelled below the 

 ligature, or in the part furthest from the heart; 

 while arteries, with a like ligature, swelled on the 

 side next the heart. Combining these facts with 

 the direction of the valves, he came to the conclu- 

 sion that the blood is impelled by the left side of 

 the heart in the arteries to the extremities, and 

 thence returns by the veins into the right side of 

 the heart. He showed, too, how this was confirmed 

 by the phenomena of the pulse, and by the results 

 of opening the vessels. He proved, also, that the 

 circulation of the lungs is a continuation of the 

 larger circulation ; and thus the whole doctrine of 

 the double circulation was established. 



Harvey's experiments had been made in 1616 

 and 1618 ; it is commonly said that he first pro- 

 mulgated his opinion in 1619 ; but the manuscript 

 of the lectures, delivered by him as lecturer to 

 the College of Physicians, is extant in the British 

 Museum, and, containing the propositions on which 

 the doctrine is founded, refers them to April 1616. 

 It was not till 1628 that he published, at Frankfort, 

 his Exercitatio Anatomica de Motu Cordis etSan- 

 guinis ; but he there observes that he had for above 

 nine years confirmed and illustrated his opinion in 

 his lectures, by arguments grounded upon ocular 

 demonstration. 



