SECT. XVII. PHYSIOLOGY. 139 
cccxL. Air expired from the lungs, contains 
the same proportional quantity of oxygen as 
before inspiration; this being the case, in what 
does the absorption of oxygen consist ? 
cccxLI. Again, by agitation of venous blood 
in a bottle containing atmospheric air or oxygen 
gas, the blood assumes its bright arterial hue, the 
oxygen is changed into carbonic acid,* but the 
volume of air remains the same, at least I have 
never been able to observe the slightest dimi- 
nution of air; and I have often repeated this 
experiment. The chemical results, and the co- 
loration of the blood, being in every respect the 
same aS in respiration, is it sound reasoning to 
ascribe to the blood the power of absorption, while 
it is contained in the veins, which power is lost 
when it is abstracted from them. Abernethy has 
even maintained, that expired air is increased in 
volume. 
cecxLut. The absorption of oxygen was in- 
tended to explain the generation of animal heat ; 
but as it has failed in this, it will be as well to 
_ reject a theory contradicted by many facts, and 
supported by none. 
cecxLiu. The obvious and principal effect of 
respiration, is to abstract the carbon contained 
in the venous blood, in its passage through the 
capillaries of the lungs; the blood is therefore 
decarbonized by respiration, and not oxygenized, 
as the pneumatic physiologists have asserted. 
