€ Of the Circulation of the Blood . 
fent figure appears, are only arteries elongated ; and as 
they generally divide into branches that efcape the fight, 
it is very difficult to determine where the arteries end, or 
where the veins begin. If in the tail of this.fmall fifii, 
the whole bulk of which was no bigger than that of 
fig. 32. and confequently under half an inch in length, 
34 diftindt circulations of the blood could be feen, how 
incredibly numerous muft that of the circulation be in 
an human body ? nor is it to be wondered at, when we 
fee it iffiue forth at every prick of a pin or needle. In 
this confideration he alfo adds, that he is fully con¬ 
vinced in a fpace no bigger than his fore finger nail, 
a thoufand diftindl: circulations of the blood are per¬ 
formed. 
Mr. Leeuwenhoek obferved the motion of the blood 
in a fmall veffel, in the tail of a tadpole, fomewhat 
wider than to admit a red globule thereof, as A and B, 
fig. 35. which veffel is called an artery, through which 
the blood coming from the heart, in the direction A B, 
is impelled with great fwiftnefs, and divided at B into 
two branches, B C and B E, which are again united at 
D, and continue fo to F, where they are again divided 
into two other branches F G and F I running crooked 
- 
till they are again united at H, where they formed a 
fomewhat larger veffel as FI K, and became bigger at K, 
for which reafon we muft call the blood veffels ABC, 
D F G, and A B E F I, arteries d , becaufe they convey 
the blood to their greateft diftance from the heart at G 
and I, and the blood veffels G FI K, and I H K, veins, 
becaufe they return the blood to the heart again. 
* In another place he faw the blood running in an ar¬ 
tery, large enough to admit about 20 red globules ® at 
once; this was a great artery in proportion to that be- 
fore- 
f Arc. Nat. Epift. 119, € Phil, Tranf, No, 260. 
