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This change takes place fo rapidly, that it requires 
great expedition to apply them to the microfcope 
loon enough to obferve it. 
I have obferved the Janies or blood of a flirimp, 
by cutting off its tail, and found veflcles in it fimi- 
Jar to thofe of the lobfter, which have been a fhort 
time expofed to the air. But I never could apply the 
blood fo as to fee them in their flat form ; but, flnce 
they changed by expofition to the air, I conjecture 
•that like them they were flat in the blood veflels ; 
but being more fufceptible of changes from the con- 
tact of air, they were corrugated before I could get 
them applied to the microfcope. 
The ingenious Leeuwenhoeck has obferved that 
in the blood of a grafliopper, its veficles or glo- 
bules, as he calls them, are green. I have feen 
the lame circumflance in the white caterpillar, 
whole ferum appeared green when in its veflels ; 
but when let out from this animal or from a 
grafliopper, the colour cannot be diltinguilhed. 
The fmalleft animal in which I have difcerned 
thefe veficles is an infect no bigger than a pin’s 
head, that is feen almolt conftantly in the river 
water which we have in London. This infeCt, 
which is a fpecies of the Monoculus, being put 
into a concave glafs with a little water, and the 
rays of the fun being made to pafs through it, 
the heart may be feen to beat, and the tranf- 
parent blood or Janie s found to have a few velicles, 
which appear to move one after the other ; being 
made viflble, though tranfparent, by the light 
palling in fuch a manner as to be refraCted by 
them. 
Since 
