1 2 Of the Circulation of the Blood. 
redtly face the eye ; thofe about c were {freight before 
the eye, and for the moft part a little clear fort of light 
in the middle, larger in fome than others. 
Mr. Leeuwenhoek, likewife, placed fome of the blood 
of a very finall butt before the microfcope, which was 
not mixed with any liquor, only the particles lay in their 
ierum, and are reprefented by fig. 41. 
Thofe particles of the blood, which are diftinguifhed 
by fhining fpots in the middle, are delineated fig. 42, 
Mr. Leeuwenhoek profocuted this enquiry yet farther, 
with a greater magnifier than he had hitherto ufed, and 
fo he plainly made out the oval particles; now the 
greater the magnifying power of the glafs, the fwifter 
does the circulation of the blood appear and having re¬ 
tarded this motion, he employed two or three feconds of 
time, in obferving the little veins, and found, that in fe- 
veral fmali veffels, the oval particles were fo broke, that 
he could neither fee them, nor thofe, of w T hich fix confti- 
tuted a particle of blood, but only a fimple fluid of a 
faint colour, running along the veffels ; but in a great 
artery at the tail, the blood mov’d fo flowly, that he 
could eafily difcern the particles were oval; and not only 
fo, but he likewife perceived more clearly than before, 
the globules that conftituted the oval parts, if not al¬ 
ways, yet at leaft for the moft part, as reprefented in 
%• 43 - 
How veinous blood may become arterious without 
being firft in the heart, appears by the following experi¬ 
ment. Suppofe A B, in fig. 44, to be a vein, in which 
the blood view’d through the microfcope, paftes with 
great celerity from B to A; from this vein proceeds 
two finall branches, C and D, which unite between E 
and F. Again fuppofe HI to be an artery, in which 
the blood moves upwards with equal fwiftnefs from H 
to 
