[ 467 ] 
firft been faturated, have found thofe Stones commonly 
to have been but about one half part, and fomeof them 
no more than a fourth part, heavier than an equal bulk 
of Water. From whence it has been too haffily 
concluded, that thefe Stones have very improperly 
been called by that name, as not at all approaching 
to the Specific Gravity of even the .lighted real 
ftones that we have any account of. 
The Calculus Humanus and Animal Bezoar ap- 
proach nearly to each other in their Specific Gra- 
vity. 
Mr. Boyle has taken notice of the great difference 
to be found between the gravity of the true and the 
fa&itious Crabs- eyes. It is ft range that the fa&itious 
fhould be made of fuch materials as can bring them 
fo near to the mean gravity of true ftoncs : and 
this confideration may deferve the attention of thofe, 
who may think that any praticular dependence is to 
be had upon the ufe of thefe bodies in medicine. 
Dr. Jurin was the firft who carefully examined 
the Specific Gravities, of the different parts which 
compofe Human Blood ; and his experiments were 
performed with the greateft accuracy. It may be 
obferved, that the Blood is, by an eafy analyfis di- " 
vided into Serum and CraJfamentUm j and the Crajja- 
mentum again into the Glutinous and the Red globular 
parts, whofc Specific Gravities are the greateft. It 
had before thefe experiments been the general re- 
ceived opinion, that the globules of the Blood were 
lighter than the Serum 5 and this indeed feemed to 
follow from Mr. Boyles Experiments in his Natural 
Hiftory of Human Blood > from which he deduced 
the Specific Gravity of the mafs itfelf, to be to that 
of 
