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XXXVI. Experiments on Atnmal Fluids in 
the exhaufied Receiver. By D. Darwin, 
M. D. of Litchfield. Communicated by 
Dr . Franklin. 
Redde, March 24, V ■ A HE antient opinion, that air 
I774 ' X. exifts in Tome of the blood- 
veffels, was exploded by the difcovery of the cir- 
culation. Bat many of our modern theories feem to 
have conceived, that an elaftic vapour of fome kind 
exifts in the blood-veffels, as they have afcribed the 
lunar and equinoctial difeafes to the variations of 
atmofpheric preffure. 
This opinion feems to have arifen from obferving, 
that the fkin rifes, and that the veffels are diftended, 
even to burfting, under a cupping-glafs ; when the 
preffure of the atmofphere is taken off from one 
part, and continues to adt on all the remaining fur- 
face of the body : and would indeed, at firft light, 
appear to be demonftrated by the following experi- 
ments. 
About four ounces of blood were taken from the arm 
of one of the attendants, and immediately put under 
the 
