Royal Society. 449 
and tirc^Jood-vefifels GH K and IH K veins, becaufe tbey return 
the blood to the heart again j in another place M. Lee-wenhoek 
law theblcod moving in an artery, which was fo large, as to admit 
about 20 of thelcred globules at once , this was a great artery in 
comparilon of thele abovementioned, and in this the blood mov'd 
very flowly, afmall portion whereof is delineated as LM, Fig. 12. 
out of this blood- veiTel proceeded a lefler, as MO 3 the blood in 
the veflel from L to M had not fo quick a motion, as it had m 
others, becauie the blood in the veffel at R did in a manner 
ftagnate, infomuch that no feparated parts could be di{cerned in 
the blood, for it appeared there of one uniform red colour, yet 
m the blood-veflel M O the circulation was as fwift, as in any 
other veflel j that the blue fpots occafioned by a fall or bruife is 
not ftagnated blood, which before it begins to corrupt, perfpires 
thro' the fkin together with the fweat, M. Lee-wenboek was 
convinced by the following obfervation j the blood at K being thus 
without the leaft motion, it was by every pulfation of the heart 
impelled upwards, from N to P, and the next moment it recoiled 
back again, and thus backwards and foi-ward;s with an undulatory 
motion J as is known, if we ufe never fo much violence in preiiing 
water, yet we cannot prefs it clofer than it was before- io the 
blood being now impelled forwards through the heart, cannot be 
comprefled into a lefs lpace3 this being fo, we muii: conclude, 
that the tunic of the blood-veflels between N and P, and alfo 
fom^ewhat below N, is dilfended by every pulfation of the heart 5 
and as foon as this uncommon diftenfion is performed, fo foon 
alio does the tunic of the vef[el contract itfelf again, whereby the 
blood that was thus puflied forwards, is forced to run back again: 
M. Leewenhoeky after fome time, obferved the blood begin to move 
from P to R after fuch a manner, as to be puflied back again, 
and he alfo judged that the blood-veflel marked MO was during 
his obfervation a little more extended, and by coniequence more 
blood ran thro' it, than when he firft began to look upon it 3 the 
blood in the vcffel N S, wherein there was little or no motion 
before, did now run as fwift, as it did in any other veflel 3 the 
blood-veffel PQ^, which wasfo llnall, that but one fingle parti- 
cle of the blood could pafs through it at once, and wherein at his 
firft viewing it there was not the leaft motion to be difcerned, 
now alfo began to flow 3 yet the particles of the blood, that at 
firft paffed through it, were but few in number, and conlequently 
farafunder3 further all the blood from P to R was put into 
motion, as well by being pufl^.ed forwards, as by recoiling back 
again, and that at every pulfation of the heart ; In thefc obier- 
VoL. III. L 1 1 vations 
