138 



DISCOVERY 



CH. 



numerous observations, I thought I had attained to 

 the truth." 



For nine successive years Harvey expounded his 

 views on the circulation of the blood, and demonstrated 

 the anatomical and experimental evidence on which his 

 conclusions were based, in his lectures at the Royal 

 College of Physicians. Only after this probationary 

 period, did he give his discoveries to the world in a 

 little book of 76 pages, published in 1628, on the 

 Movements of the Heart and of the Blood. In this 

 treatise Harvey established absolutely the fact of the 

 circulation of the blood, and the fact that muscular 

 action of the heart causes this movement. But he was 

 unable, from his want of a microscope, to indicate the 

 precise path along which the blood travels from the 

 terminal arteries to the commencing veins. 



The large artery from the heart gives off branches to 

 various parts of the body, and these branch off again into 

 small arteries in different organs. Similarly, small 

 veins carrying blood back to the heart unite to form 

 large veins. How the blood passed from the small 

 arteries to the small veins could only be conjectured by 

 Harvey, and was not discovered until three years after 

 his death. He concluded that the blood passes from 

 the arteries to the veins mainly by percolation, as water, 

 to use his own illustration, percolates the earth and 

 produces springs and rivulets. No microscope in his 

 time was powerful enough to enable him to see the 

 meshwork of very minute tubes the capillaries which 

 can now be observed easily. 



Improvements in the microscope enabled Malpighi in 

 1660 and Leeuwenhoek in 1688 to demonstrate the 

 completion of the circuit of the blood by microscopic 

 observations of the movement from arteries to veins 



