Certain Pojitions laid doivn hy the Author, refpcSling the Circula- 

 tion of the Blood in an Human Body, with his Opinioji refpeSling 

 the manner of exhibiting the Circulation hy the Injedion of 

 Quickjilver. 



A HAVE heard it faid that the blood is circulated throughout our 

 bodies fourteen times in the Ipace of an hour; but no reafons have 

 ever been alligned to me from whence this conclulion was drawn. 



This fubje6l has been much in my thoughts, efpecially fmce I 

 have {een fo much of the circulation myfelf ; and I have been con- 

 lidering tliat the blood which is carried to the extremities of our 

 feet, mull pafs through nearly three times the dillance from the 

 heart as that which is circulated to the top of the head. For let us 

 fiippofe the extremities of the feet, in any human body, to be four 

 feet and an half dillant from the heart, we muft at the fame time 

 reckon the top of the head, in the fame body, to be only one foot 

 and an half dillant from the heart; and, confequently, the blood 

 which palles through the head may perform three circuits, while 

 that which is carried to the feet is performing one. Hereupon I 

 have confidered with myfelf, how to lay down certain axioms or 

 pofitions whereby I might inveftigate this matter, upon fufficient 

 grounds, without paying any regard to bare affertions; and only 

 admitting this lingle faft, that the blood adlually does circulate to 

 and from the extremities of the hands and feet, as well as the reft 

 of die human body. 



Upon relle6ling how fwift a motion the blood appears to have in 

 the arteries, when viewed by the microfcope, though when exa- 



VoL. H. S s 



