Of the Circulation of the Blood. y 
fore-mentioned, a fmall part of which is delineated at 
L M, fig. 36. out of which proceeded a leffer, as M O. 
The blood in the veffel from L to M, had not fo 
quick a motion as it had in others, becaufe the blood 
in the veffel at R, did in a manner ftagnate, info- 
much, that no feparated parts could be diftin&Iy feen, 
k appearing there of one uniform red colour ; yet in 
the veffel M O, the circulation was as fwift as in 
any other veffel. That the blue fpots, occalioned by a 
fall or bruife, is not ftagnatfid blood, which perfpires be¬ 
fore it begins to corrupt through the fkin with the fweat, 
Mr. Leeuwenhoek was convinced of by the following 
obfervation. The blood at R being thus without the leak 
motion, it was by every pulfation of the heart impelled 
upward, from N to P, and the next moment recoiled 
back again, and this alternately with an undulatory mo¬ 
tion ; as is known if never fo much violence be ufed in 
prefling water, yet it cannot be preffed clofer than it was 
before; fo the blood being now impelled forwards thro’ 
the heart, cannot be compreffed into a lefs fpace; this 
being fo, we muff conclude, that the tunic of the blood 
veffels between N and P, and alfo fomewhat below N, 
is diftended at every pulfation of the heart; and as foqn 
as this uncommon diffention is performed, fo foon alfo 
does the tunic of the veffel contract itfelf again; where¬ 
by the blood, that was thus puflied forwards, is forced to 
run back again. After a fhort fpace of time he faw the 
blood begin to move from P to R, in fuch a manner as 
to be pulhed back again, and that during his obfervation, 
the blood veffel M O, was a little more extended ; con- 
fequently more blood ran through it than when he firft 
began to look upon it; the blood in the veffel N S, 
wherein was little or no motion before, now ran as fwift 
as in any other veffel : the veffel P Q^was fo fmall, that 
B 4. only 
