Of the Circulation of the Blood. 11 
from the arteries; on one fide of a little bone, runs an 
artery, and on the other a vein, correfponding thereto ; 
and finding it eafy to extend the tail, he accordingly 
ftretched it in breadth, equal to what the fifh gives in 
fwimming, that he might the better obferve the motion 
of the blood in thefe extended veffels, and found when 
the fifh did not move, feme of thofe fmall veffels, which 
before received three particles in breaft, being now 
ftretched out with the tail-fin, which they run a-crofs, 
did not only admit no more than one particle, but like- 
wife thefe particles did not move fo faff, as when the 
veffels were not extended ; and in fome places were at 
fuch a diffance, that one or two more might lie in the 
intervals, but could not from all this determine, that 
the particles were perfectly oval f . 
But to trace the matter further, he took the blood 
running from a live falmon, g when cut into pieces, and 
put it into a glafs tube, no larger than a fmall quill, 
which in a fhort time congealed; but when it became 
partly fluid again, he put it into a fmalter glafs tube, 
and having placed it before his eye in the microfagpe, 
the particles being in motion, fome of them appeared of 
a flat oval figure, and others, which fhewed themfelves 
fide ways to the eye, feernd a little thick, and thofe 
whofe fides did not diredtly face the eye, feem’d a little 
broader, without the leaf!: appearance of any globular 
form. Mr. Leeuwenhoek alfo put fome of the fame 
blood upon a very clean glafs, and where the particles lay 
thin, he perceived them oval ; nay in feveral ovals he 
difeovered globules, and in fome few fix globules. 
Fig. 40. A B C D reprefent the oval particles of the 
blood of a falmon, that weighed 30 pounds ; A B, th« 
particles that appear’d flat and broad, but did not di¬ 
rectly 
[ Ate. Nat. Epift, 128, s Phil. Tranf. 263. 
