( 902. ) 
great Apparatus of Air-Veflels to be for a Fan to cool 
the Mais of Blood, and that rhe Air returns unalrcr'd, 
and not capable of making any great alteration, being 
denied any ingrefs into or mixture with the Blood. The 
Oofervation is certain and unerring, that the Venal 
Blood as it pafles the Right Ventricle at its entrance in- 
to the Lungs is of a very opake and blackifh Complexi- 
on, and in its paflage through the Lungs before it comes 
to the Left Auricle, is changed into a very florid and 
bright Red. I have often obferved that Perfons that 
have Vomited Blood upon a Rupture of fome Capillary 
Veflels of the Lungs, have fentup a very froathy or fpu- 
mous Blood,and at the fame time of a bright Scarlet Red: 
That it was froathy, argues that the Air had incorpo- 
rated with it; that it was Red was due to the tingeing 
power of the Air. To expeft that this change (hould 
be made in the Heart by any Local Ferment, or flamma 
vitalis is fruitlefs; becaufe we find it performed before 
its arrival there; the ftru£ture of the Heart denoting that 
Engine to be principally made for projecting the Blood 
in order to a Circulation through thofe various Arteries 
or Pipes which are branched from the Heart. Let us 
therefore examine the ftrufture of the Lungs, and very 
briefly confider them, we fhall foon difcover it to be a 
Pneumatic Engine made principally for taking in Air, 
and that in great quantities, which a Remark in the 
Fourth Corollary does much favour. It s true, we may 
call the Lungs a Contexture of Veins, Arteries, Nerves, 
Lyrxiphasdu&s, @V. and that thefe do very much make 
up the Parenchyma ( as fome do ufe the word*) of the 
Lungs ; but yet we fhall find the great bulk of the 
Lungs to be Veficular : It feems to me to be a Continua- 
tion of the Afpera Arteria, or Wind-pipe, divided and 
fubdividcd into many Branches, and thefe ftill fpun out 
into lefler and leffer Pipes, all of them hollow; the far- 
ther they run the thinner their fides do grow, which 
upon 
