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Laftly, if we advert to the blood-veflels in this eel, in and near 

 the heart, where probably the blood is not protruded the fourth part 

 of an inch before it is carried back to the heart, we fhall find that 

 in thofe veflels in and near the heart, the circulation may be per- 

 formed an inconceivable number of times in an hour, 



I have many times endeavoured to fee the current and circulation 

 of the blood in quadrupeds, which always live on land ; but I never 

 could difcover it: among birds, I found a fpecies in which I could 

 moll plainly fee the motion of the blood, but I could not diflin- 

 guilli the complete circulation, by reafon of the great number of 

 blood veflels, which caufed the part I viewed to appear red.* 



Now, if we take for granted that in our own bodies the blood is 

 carried through the arteries with the fame degree of fwiftnefs as in 

 eels, and that the extremities of the feet or toes are diftant from the 

 heart in any human body four feet and an half, or fifty-four inches, 

 making the blood perform a circuit of ] 08 inches, it will follow 

 that the blood is carried to the extremities of the feet, and brought 

 back to the heart, in the fpace of an hour, only two times or circuits, 

 and two-thirds of another circuit. 



In the next place, fuppofing the blood-veflels at the extremities 

 of our fingers to be two feet and three-quarters, or 33 inches, 

 diftant from the heart, making a circulation of 66 inches, we fliall 

 find, by the fame mode of computation as before, that here the cir- 

 culation can be performed 4 Vt times in an hour. By the fame rule^ 

 in thofe blood-veflels in the breafl:, and other parts in the body, only 

 twelve inches diftant from the heart, the circulation may be per- 

 formed twelve times in an hour ; and in thofe veflels in the far- 

 theft part of the head, which may be fuppofed 18 inches diftant 

 from the heart, the circulation may be performed eight times in an 

 hour. 



* A ceck's comb and gills, Vol. I. p. CO. 

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