282 
ploy that term ; but the physiologist farther requires 
to know, by what organs or vessels it is removed, 
in what course it is conveyed, and what uses it is 
destined to serve. On none of these points, how- 
ever, does he gain any information ; and all the ana- 
tomical knowledge which he possesses of the struc- 
ture of the lungs, and of the properties of the living 
absorbent system, is adverse to such a doctrine. 
Should he apply to the chemist for a solution of his 
difficulties, he is told that oxygen does not chemical- 
ly combine with other bodies, unless it be brought 
into actual contact with them ; and he knows, 
that, in the present case, this contact is impossible, 
because the membranes, both of the air-cells 
and blood-vessels, are interposed between the air 
and the blood in the lungs. Even if, contrary 
to all experience and analogy, he were to con- 
cede to the chemist the existence of pores or 
other passages in the cells and blood-vessels, 
through which this oxygen might be attracted and 
combine with the blood, he is equally embarrassed to 
discover the reason or mode in which it is again so 
speedily expelled, or what useful purpose it can 
serve, since no portion of it is permanently retain- 
ed. The science of chemistry furnishes no example 
of similar operations, of fluids which attract gases 
and combine them, so as to reduce their elasti- 
city, and then, without any apparent change of con- 
dition or circumstances, almost instantly discharge 
them in a new and elastic form. 
574. If, farther, we compare the results of the 
