( 324 ) 



But, if we make a calculation on thole veflels in the body which 

 are \\ ithin twelve inches diltancc from the heart, and confider more- 

 over how many veflels there are very near to the heart, and even in 

 the heart itfelf, here we Ihall find that the circulation may be per- 

 formed in a very fhort fpace of time. 



Upon the whole, it may probably be true, that in an hour's time 

 there pafles througlj the heart fourteen times as much blood as the 

 whole body contains: but it cannot be faid that all the blood in 

 our bodies performs its circulation fourteen times in an hour, foraf- 

 much as we have feen, from what is before laid down, that in many 

 parts of the body this cannot be the cafe; and in particular in the 

 feet, where it appears that the blood can, in an hour's time, perform 

 no more than two complete circulations, and two-thirds of ano- 

 ther. 



I am aware, that many may objecfl to thefe my pofitions, refpedl- 

 ing the circulation of the blood, and fay that I have feen it, in frogs 

 and in fi flies, only at the extremities of their bodies, where the mo- 

 tion of the blood is exceedingly flow; but that, if it could be feen 

 in the veflels near the heart, there its motion would be found to be 

 much fwifter : and, in proof of thefe opinions, they reafon 'by 

 analogy to what we obfene in the motion of a Iblid body in the air, 

 fuch as an arrow or a bullet, which moves with great fwiftncfs when 

 firfl difcharged, but whofe velocity continually diminiflies: fo, fay 

 they, the blood mufl move with much greater fwiftnefs in the veflels 

 next the heart, than in thofe vefl^els of the fame flze which are near 

 the extremities. 



To this I anfwer, that the motion of the blood in our bodies, or in 

 the blood-veflels in fiflies, has not any analogy to the motion of a 

 folid body in the open air; and in proof hereof I have cauled a 

 figure to be drawn, which may be feen in Plate \X.fig. 4. A B C 

 D E F, which we will fuppofe to reprefent a leaden tube, from 

 whence various fmaller tubes branch forth, as at B G, C H, D I, 

 E K, and F L, and that this tube and all its branches are filled with 



