2 o Of the Circulation of the Blood. 
forwards In its Aiding focket I K, or elfe by pulling the 
fald focket farther from, or pufliing it nearer to, the 
pillar of the microfcope, by which means, you may 
with the greateft eafe imaginable, examine all the bldod- 
veflels in this tranfparent flap or piece of {kin, by fitting 
at a table before a window, and dire&ing the illuminat¬ 
ing glafs, fo as to fling the rays of light immediately 
under this part of the {kin. 
If the fun fhines, and you have the folar apparatus 
before deferibed, ferewed ready in the window fhutter, 
apply the microfcope and frog to the folar part as before 
{hewn, and after having dire&ed the fun’s rays through the 
tube, upon any part of the fkinny flap L R S M, and placed 
the fereen at about four or five foot from the machine, 
fo as to receive the fun’s rays, and adjufted the objedl 
to the focus of the magnifier, and diftance of the fereen, 
you will have reprefented on the fereen, a moft beauti¬ 
ful pidfure of the veins and arteries in the {kin, with the 
blood circulating through them; in the arteries you may 
plainly perceive the blood flopping, and as it were re¬ 
ceding a little at each dilatation of the heart, and then 
immediately rufhing forwards again at each contraction; 
whilft in the veins it rolls on in a continual current, with 
inexpreffible rapidity; and when the arteries are very 
much magnified, if you remove the fereen to a confider- 
able diftance, the alternate expanfion and contraction of 
their fides are very vifi^le. 
When you have confidered this as long as you think 
needful, open the abdomen, and extend the mufcles be¬ 
fore the microfcope, by means of the two fi{h-hooks, as 
before in the extenfion of the {kin, and you will with 
pleafure view their ftru&ure, which confifts of num¬ 
bers of tranfparent firings or fibres, lying parallel 
tp 
