C 309 ] 
As to their fhape, I have already mentioned that 
they are flat in all animals, even in the human fub- 
■je£t ; of which any one may be convinced by repeat- 
ing the following experiments. 
Experiment 1 . Take a (mall quantity of the 
ferum of human blood, and (hake a piece of the 
craflamentum in it, till it is coloured a little with 
the red particles ; then with a foft hair pencil fpread 
a little of it on a piece of thin glafs, and place 
this glafs in the microfcope in fuch a manner as 
not to be quite horizontal, but higher at one end 
than the other, by which means the ferum will 
flow from the higher extremity to the lower, and as 
i-t flows, foms of the particles will be found to fwim 
on their flat fides, and will appear to have a dark fpot 
in their middle ; others will turn over from one 
fide to the other as they roll down the glafs. No 
perfon who fees them turn over can doubt of their 
being flat ; he will lee them in turning have all the 
phafes that a fiat body has ; firft he will lee them 
on one fide, then rife gradually upon their edge, 
and turn over to the other fide. 1 have in this wav 
fli ewed their figure to a number of curious perfons, 
and particularly to many ftuder.ts of anatomy, who 
have attended ledtures in London within the lait 
fix years. 
If, in (lead of ferum, the particles ftiould be di- 
luted with water containing rather more fait than 
ferum does ; or if, inftead ot human blood, that of 
an animal with larger particles be ufed : then they 
will fometimes be feen not -only flat, but a little 
bended, like a crooked piece of money. 
S f 2 
Thefe 
