Editor's Introduction ix 



simple, for without this knowledge it is no exaggeration 

 to say that a real understanding of any important 

 function of the human body was impossible. And 

 hence it has been contended with much force that not 

 only the science of physiology, but the scientific practice 

 of medicine date from this discovery. " To medical 

 practice," says Sir John Simon, "it stands much in the 

 same relation as the discovery of the mariner's compass 

 to navigation ; without it, the medical practitioner would 

 be all adrift, and his efforts to benefit mankind would 

 be made in ignorance and at random. . . . The 

 discovery is incomparably the most important ever 

 made in physiological science, bearing and destined to 

 bear fruit for the benefit of all succeeding ages." l 



When Harvey first approached the subject, there 

 were all kinds of crude and fantastic ideas regarding 

 the functions and uses of the heart, bloodvessels, and 

 blood that the heart was the workshop in which 

 were elaborated the spirits, a due supply of which was 

 necessary for many parts of the body ; that from the 

 heart the arteries carried spirits, the veins nutriment to 

 the different parts of the body ; that the arteries con- 

 tained blood and air mixed together, or only air ; that 

 fuliginous vapours, whatever they may be, passed from 

 the heart along the bloodvessels ; that the septum of the 

 heart, by which its two sides are completely separated, 

 was riddled with minute holes, like a fine sieve, through 

 which the blood percolated from the right to the left 

 side ; again, that the heart was the organ in which the 

 heat of the body was produced. Another favourite 

 theory was that the blood moved from the heart along 

 certain bloodvessels and back again by exactly the 

 same channels, after the manner of the rise and fall of 

 the tides, to which in fact the movement was likened. 

 More curious still, even the best informed appeared to 

 believe that the arteries terminated in nerves. 



1 Harvey Tercentenary Memorial Meeting, Folkestone, September 6, 

 i 871. 



