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jfciiimals ; and thirdly, becaufe the particles of blood from which its 

 rednefs proceeds, appear much larger in fifhes, they being of a flat 

 and oval fliape; whereas, on the contrary, as far as I could judge 

 from my eye, they, in this animal were fpherical. I ufed every 

 means I could devife to fee the compleat circulation of the blood, 

 namely, that one of the fmalleft of thofe veffels which we call veins, 

 arofe from another which is called an artery, and afterwards con- 

 veyed its contents into a larger vein ; but this I found to be impoffi- 

 ble, for when I followed the courfe of the artery, until it became fo 

 fmall as only to admit one or two globules to pafs through it at a 

 time, I then loft fight of it. If this artery, throughout its circuit, had 

 not been fmaller than the twenty-fifth part of an hair, I do not doubt 

 that I could have feen the whole circulation ; but as thefe veffels 

 were at their extremities diminiflied to a much lefs fize, and the 

 membrane of the wing was covered with a kind of fcales, I could not 

 (as I have before faid) follow with my eye thofe minute ramifica^ 

 tions. I perceived, however, in many places, an artery and a vein, 

 placed cloi'e bcfide each otlier, and of a fize large enough to admit 

 the pallage of ten or twelve globules of blood at the fame time ; and 

 in this artery the blood was protruded or driven forward with great 

 fwiftnels, and flowed back through the vein, which was a moft plea- 

 fmg fpeclacle to behold. 



I could alfo moft plainly perceive in the arteries, the rifing, or pul- 

 fatioii, caufed by the motion which the blood receives from the heart ; 

 tlicfe pulfations were fo rapid that I judged feven ftrokes were per- 

 formed in a fccond of time. 



The worm, or fmall animal which is produced from the fpawn of 

 frogs, and is called a tapdole, afforded me a ftill more diftin6l view 

 of tiiis fubje6l; for, upon placing one of them, which was newly 

 hatched, before the microfcope, I could diftinftly perceive the wliole 

 circuit of the blood, in its paflbge to the extremities of the vellels, 

 and in its return towards the heart. But I mull here obfcrve, (as 



