BLOOD, ARTERIAL AND VENOUS. <S9 



the red, arterial, and its greater deficiency in the purple, venous 

 blood. 



The action of oxygen gas on venous blood, by producing an 

 immediate change to a scarlet-red color, has been proved by 

 Priestley, Hazzenfratz, and Davy. The effect of atmospheric 

 air is similar. 



Venous blood, exposed to the action of nitrogen, continues 

 unaltered in color. 



When nitrous gas is applied, venous blood becomes a deep 

 purple, which may arise from a further neutralization of 

 oxygen ; for with nitrous oxide it is a bright purple ; with 

 carbonic-acid gas a brownish-red colour, as observed by Dr. 

 Beddoes. 



Azotic gas, and carbonic-acid gas, gradually afford to arterial 

 blood the dark color of venous ; even the removal of pressure 

 produced the change in color, by placing arterial blood in 

 vacua (Priestley) ; consequently, the appearance of color may 

 be in such instance occasioned by a change in the surfaces 

 exposed by the atoms, on altering the position of their poles, 

 from new acquisitions of additional constituents, or from the 

 abstraction of one, or more : in either case, the position of the 

 poles may be varied, and a fresh surface exhibited, rendering a 

 difference of colour evident. 



Chlorine, when poured on venous blood, produced a deep, 

 almost Hack, colour (Hazzenfratz) ; while muriatic acid ef- 

 fected no change (Fourcroy). See Dr. Thompson. 



The predominant constituents affording COLOUR, occupy the 

 upper hemisphere of the compound spherical atoms of liquids. 

 The application of the microscope to fluid bodies while under- 

 going change of colour, from addition of constituents, may 



afford much information. 







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