102 WILLIAM HARVEY 



to open and shut the pores and vessels, precisely as in 

 case of a sponge, and of parts having a spongy structure, 

 when they are alternately compressed and again are suf- 

 fered to expand. The liver, on the contrary, remains at 

 rest, and is never seen to be dilated or constricted. Lastly, 

 if no one denies the possibility in man, oxen, and the larger 

 animals generally, of the whole of the ingested juices pass- 

 ing through the liver, in order to reach the vena cava, for 

 this reason, that if nourishment is to go on, these juices 

 must needs get into the veins, and there is no other way 

 but the one indicated, why should not the same arguments 

 be held of avail for the passage of the blood in adults 

 through the lungs ? Why not maintain, with Columbus, that 

 skilful and learned anatomist, that it must be so from the 

 capacity and structure of the pulmonary vessels, and from 

 the fact of the pulmonary veins and ventricle corresponding 

 with them, being always found to contain blood, which 

 must needs have come from the veins, and by no other 

 passage save through the lungs? Columbus, and we also, 

 from what precedes, from dissections, and other arguments, 

 conceive the thing to be clear. But as there are some 

 who admit nothing unless upon authority, let them learn 

 that the truth I am contending for can be confirmed from 

 Galen's own words, namely, that not only may the blood 

 be transmitted from the pulmonary artery into the pul- 

 monary veins, then into the left ventricle of the heart, and 

 from thence into the arteries of the body, but that this is 

 effected by the ceaseless pulsation of the heart and the 

 motion of the lungs in breathing. 



There are, as everyone knows, three sigmoid or semilunar 

 valves situated at the orifice of the pulmonary artery, which 

 effectually prevent the blood sent into the vessel from 

 returning into the cavity of the heart. Now Galen, explain- 

 ing the use of these valves, and the necessity for them, 

 employs the following language: 1 "There is everywhere a 

 mutual anastomosis and inosculation of the arteries with the 

 veins, and they severally transmit both blood and spirit, by 

 certain invisible and undoubtedly very narrow passages. 

 Now if the mouth of the pulmonary artery had stood in 



1 De Usu partium, lib. vi, cap. 10. 







