( 328 ) 



cannot fay that I R is an artery and K L a vein, becaufe in tliofe 

 veflels, which are villblc by the naked eye, the blood is not carried 

 from and alfo back to the heart in circvdation ; for \\ here I have 

 obfervcd thefe arteries to liave a bend, I have often perceived that 

 they were fpread into branches, as is here flicwn at L, and thcfe 

 again into fmaller branches; fo that at firft fight we might fay that 

 the circulation is performed in JNI N O, and that M P Q, N P Q, 

 and O P Q, are veins. 



I was formerly of opinion, that the blood which, in the arteries, 

 is carried to the extremities of the body, did, in its parage, gra- 

 dually lofe part of its thinner juices, by the continual puliation of 

 the blood forcing thofe juices through the coats of the arteries. 

 But, after frequently contemplating the circulation, I am aflurcd 

 that the coats of the arteries are lb formed, as not to permit the 

 leall particle of the blood to pals through them, until thofe arteries 

 become divided into fuch very fmall branches, as give paflage to no 

 more than one, two, or three globules of blood at a time ; at which 

 places the circulation or return of the blood to the heart takes place ; 

 and here, through the extreme thinnefs of the coats of the velfels, 

 the liner juices of the blood may find a palliige on all fides for the 

 nourilliment of the parts adjoining. For were it otherwife, not 

 only the external parts would want a due proportion of nourilli- 

 ment, but the circulation of the blood itfelf could not be performed 

 to anfwer its intent ; for the external parts of the body require the 

 greatell fupply of thin juices, by reafon of the great expence of 

 moillure they are expofed to from perfpiration and otherwife. But 

 if the blood was carried both to and from the heart in circulation 

 in the veflels, which are fo large that we can injeft quicklilver or 

 warm wax into them, and are of fuch a fize as to admit two or 

 three thoufand globules of blood, or more, to pafs through them at 

 a time, and the coats of thofe arteries being, as I conceive, fo folid 

 and- impervious that they will not fuffer the very fine juices to pafs 

 through them, the confcquence would be, that in thofe large vef- 



