114 Of viewing the Blood 
In all Enquiries of Confequence, it is bed 
to draw the Blood from a large Vein : be- 
caufe what we can gain (by the Prick of a 
Pin or Needle) from the Finger, or any fuch 
Part, iffues from lb me extremely minute 
capillary VelTels only, and perhaps is not lb 
good a Sample of the Contexture of the 
whole Mafs. Some Trials on both may 
however not be amifs, to difcover what 
Difference there is between them. 
By mingling with the Blood the lead ima¬ 
ginable Quantity of th Qpoifonous Juice which 
iffues from the Teeth of a Viper when en¬ 
raged, or from any other Animal , Vegetable, 
or Mineral , we fhall difcover its immediate 
Effedt upon the Globules; and by c on fide r- 
ing that the Alteration we obferve is wrought 
in it tho’ at Reft, we fhall be able to judge 
and calculate what Confequences muft enfue 
from fuch a Mixture with the Blood, as it 
circulates through the Veins of a living 
Creature. 
Mr. William Cowper, examining a 
Solution of Opium with ilizMicrofcope , found 
its diffolved Particles in the Shape of fringed 
Globules : whence he concludes, that fuch 
Particles circulating in the Mafs of Blood, 
may be fo entangled in its Serum, or thicken 
it in fuch a Manner, as to retard its Velocity 
when over-violent, and render its Motion 
calm and equal; whereby all painful Senfa- 
tions 
