100 WILLIAM HARVEY 



vena cava, will pursue the wisest course if they seek 

 dissection to discover the causes why in the larger and 

 more perfect animals of mature age nature has rather 

 chosen to make the blood percolate the parenchyma of the 

 lungs, than, as in other instances, chosen a direct and 

 obvious course for I assume that no other path or mode 

 of transit can be entertained. It must be because the larger 

 and more perfect animals are warmer, and when adult their 

 heat greater ignited, as I might say, and requiring to be 

 damped or mitigated, that the blood is sent through the 

 lungs, in order that it may be tempered by the air that is 

 inspired, and prevented from boiling up, and so becoming 

 extinguished, or something else of the sort. But to deter- 

 mine these matters, and explain them satisfactorily, were to 

 enter on a speculation in regard to the office of the lungs 

 and the ends for which they exist. Upon such a subject, as 

 well as upon what pertains to respiration, to the necessity 

 and use of the air, etc., as also to the variety and diversity 

 of organs that exist in the bodies of animals in connexion 

 with these matters, although I have made a vast number of 

 observations, I shall not speak till I can more conveniently 

 set them forth in a treatise apart, lest I should be held as 

 wandering too wide of my present purpose, which is the 

 use and motion of the heart, and be charged with speaking 

 of things beside the question, and rather complicating and 

 quitting than illustrating it. And now returning to my 

 immediate subject, I go on with what yet remains for demon- 

 stration, viz., that in the more perfect and warmer adult ani- 

 mals, and man, the blood passes from the right ventricle of 

 the heart by the pulmonary artery, into the lungs, and thence 

 by the pulmonary veins into the left auricle, and from there 

 into the left ventricle of the heart. And, first, I shall 

 show that this may be so, and then I shall prove that it is 

 so in fact. 



