82 ME M O IR S of the 
there is a great difference in colour between the venal and arterial 
blood 5 the former, as loon as it is let out of the vein, is of a dark 
colour, and muft be expofed to the air for Ibme time before it 
obtains a florid red, and that only in the furface contiguous to the 
air: The obfcrvation is certain and unerring, that the venal blood, 
as it paflcs the right ventricle at its entrance into the lungs, is of a 
very opake and blackiili complexion, and that in its paflage thro' 
the lungs, before it reaches the left auricle, it is changed into a 
very florid and bright red ; and it has been often obierved> that 
peribns that have vomited blood, upon a rupture of fome capil- 
lary veflels of the lungs, have difcharged a very frothy blood, and 
at the fame time of a bright fcarlet red 5 its being frothy argued an 
admixture of air, and its being red was owing to the tinging qua- 
lity of the air; to expecl: that this change fliould be made in the 
heart by any local ferment, or vital flame would be fruitlefs, be- 
caule this change is wrought, before its arrival thither, and 
becaufe the flruciure of the heart denotes it to be principally made 
for projecting the blood in order to a circulation thro' thole various 
arteries which are branched from the hearty if we confider the 
flru(Pcure of the lungs, we fliall loon dilcover them to be a pneu- 
matic engine principally defigned for taking in air, and that in 
great quantities 3 it is true, we may call the lungs a contexture of 
veins, arteries, nerves, lymph^du^ts, ^c. but we iliall find the 
greater bulk of them to be velicular, which feems to be a conti- 
nuation of the wind-pipe, divided and lubdivided into many 
branches, and thefe ftiU ipun out into Imaller and fmaller pipes, 
all of them hollow ; and the farther they run, the thinner their 
fides do grow, which, upon inlpiration do fwell and grow round, 
and upon expiration become flaccid, and abate Ibmething of that 
figure; the languiferous veflels are divaricated thro' all the lobes 
of the lungs, and very clofely accompany each Veficulay in order 
to receive Ibme confiderable benefit from it, and this appears to 
the eye ; for in an inflant, a dark and foul blood is changed into a 
bright florid red colour: Thus the very fl:ru61:ure of the lungs, 
the change of colour both in the blood and in our experiment, 
the one from a dark opake colour to a noble icarlet, the other 
fiom a pale or colourlels liquor to a rich ultramarine blue, do all 
ihcw that this alteration is owing to the air; and Dr. Shre is oF 
opinion, that hei/je arilc the great fermentations of the blood, the 
caufe of the motions and actions of the mufcles^ and that the ani- 
mal Ipirits themfelves, thole great fprings of motion, derive 
their energy and power, if not nature, from hence. 
Coi'ol- 
