f24 Letter to Governor Poinialt 



without air,) it follows that air preserves fire and flame W 

 means of acid particles j and since it preserves the life of 

 aniiiials by the operation of the very same particles whereby 

 it preserves tire and flame, it likewise follows that it pre- 

 serves the life of animals bv its acid particles. 



" Fuurthhj, The venal blood is of a deep purple colour, 

 and the arterial blood of a bright red, in all parts of the body 

 except the lungs ; and in them the blood is of a dark purple 

 colour in the pulmonary arterv, and of a bright red in the 

 pulmonary vein. Hence it follows that the blood changes 

 its deep purple colour into a bright red in the communicant 

 branches of the pulmonary arterv and vein which are spread 

 on the vesicles, and that it changes its bright red into a 

 deep purple colour in the communicant branches of the ar- 

 teries and veins of other parts. If blood be drawn out of a. 

 vein, its surface, which is contiguous to the air, will acquire 

 the same bright red colour which the blood acquires in the 

 lungs ; and if this red surface be cut ofi"with a sharp knife, 

 the blackish surface of the remaining blood, being now 

 touched and acted upon bv the air in the same manner as 

 the first, will acquire the same colour as that did ; and the 

 same change of colour will be made in the bottom of tht 

 cake, if it be turned upwards in the cup, and exposed to 

 the air; and if blood ju?t drawn be stirred and agitated till 

 the air be intimately mixed with it throughout, its whole 

 substance will soon acquire the bright red colour of arterial 

 blood. If the windpipe be stopped with a cork, and some 

 time after the operation (when the air wliich is shut up in 

 the lungs is made eflete, that is, deprived of its acid parts) 

 blood be drawn from the cervical artery, it will have the 

 same dark purple colour as venal blood. 



" Now, since from these experiments the air nnist touch 

 venal blood drawn out of the body to change its deep purple 

 colour into a bright red, and the acid parts of the air cause 

 the same change of colour in the blood in the lungs, it will 

 follow that there must be a like contact of these acid parts 

 u'ith the blood in the lungs : and since I have shown that 

 air preserves the life of animals by its acid parts, it will 

 likewise follow that the life of animals is preserved by acid 

 parts of the air mixing with the blood in the lungs. 



*' Fifthly, The bright red colour acquired by the blood 

 in the lungs, from its purity and intenseness, is the red of 

 the second order of colours in the table of Sir Isaac New- 

 ton's Optics, p. '20Q •■ but the blackish or deep purple co- 

 lour of venal l)lood turns into tais bright red without pass- 

 ing through, tne colours of blue, green, yellow, and orange, 



and 



