io Of the Circulation of the Blood. 
called a vein, and the blood coming to c, being there 
transfufed into c e, is the arterial blood, becaufe it is 
conveyed thither from the heart, it being certain that 
d c e is an artery. 
Amongft others, Mr. Leeuwenhoek had a tadpole, 
wherein he could perceive no motion at ail of the blood, 
how attentively foever he view’d it ; at firfl: there ap¬ 
pear’d no reafon for it, till upon examining this animal 
with his naked eye, he cbferved the fore part of his body 
was contracted, by which he imagin’d the heart was fo 
oppreiled, that it could not force out the blood, and 
receive it back again. Whiift he was thus contemplat¬ 
ing, the animal made a very ftrong motion; beating 
its tail about, and bending its body, by which it got 
dear of the oppreflion it was under ; and on viewing it 
again, perceived the blood to have a flow motion, and 
impulfe in feveral vefiels, which increafed till it at length 
came to its proper motion, yet not with fuch velocity as 
it would have had, if the heart or body had not been op- 
preffed. Mr, Leeuwenhoek fays, that the motion of 
the blood in thefe tadpoles, exceeds what he ever faw 
in any other animal. Fig. 39. exhibits a tadpole arri¬ 
ved to fuch a bignefs, as to ufe its hinder legs, and the 
fore legs were alfo difcernable, but yet covered with the 
fkin. 
Mr. Leeuwenhoek obferved the circulation of the 
blood in feveral butts, one of which, bating the tail, 
was but an inch in length ; the greatefl: motion of the 
blood obfervable through the fins, was on each fide the 
various little Angle bones placed therein, where the 
blood-veflels were fo large, that 25 of thofe particles 
which conftitute the blood of a red colour, could pafs in 
breadth, but difappear’d as they drew nigh the extre¬ 
mity of the fins, fmall vefiels being all along difpers’d 
from 
