Of the Circulation of the 'Blood. i 
you may behold the circulation of the blood in every 
part of the fubjedf, and in a more particular manner in. 
the tail, near k fifty vefiels prefenting themfelves at once 
to view; and alfo the pulfation of the heart; but they 
grow fo opake in a day or two, that the circulation can 
then be only feen in the fins, and at the joining on of 
the head, and in the tail. 
The circulation of the blood affords an entertaining 
fight in the thin membrane between the toes of the hind 
foot of frogs, if well expanded; and placed before the 
magnifier, the arteries and veins will be diftindtly feen. 
The blood may be retained in the lungs of frogs and 
lizards, as follows ; on making an incifion into the bodies 
of thefe animals, their lungs will ftart out, and be diftended 
with infpired air; on thefe, as quick as you can, pafs a 
waxed thread, and tie it firmly towards the upper part of 
the lobe, as near the heart as poflible ; when the lungs 
are dried, after being thus diftended, they may be placed 
in parts, between the talcs of an ivory Aider, and by 
this means you may always keep by you objedfs of the 
lungs of thofe animals, only remember to place their ex¬ 
ternal fmooth furface towards the magnifier. Thefe 
feveral parts of the lungs are very entertaining objedts 
in the microfcope. 
But the circulation of the blood is no where feen with 
fij much fatisfadlion as in the mefentery of a frog. For 
which I have contrived an eafy method to hold the animal 
during the operation, as will be feen in what follows. 
k Arc. Nat. Epift. 112. 
The 
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