On Respiration and Animal Heat. 23 
outwards so as to permit the escape, but 
bar the entrance of any gas. These pores, I 
am afraid, would be so constantly filled with 
liquid, that it would obstruct, if not altogether 
destroy, their proper function. 
The whole scheme is evidently attended 
with insuperable difficulties. But it will be 
urged, that the blood has a known affinity for 
oxygen; witness the florid colour which it 
always assumes in oxygenous gas. True; but 
does this prove that oxygen has combined 
with the blood, and entered into that liquid, 
or does it prove that some particles of the 
blood have combined with oxygen, and made 
their escape from the surface of the liquid, 
which assumes a vermullion hue after their de- 
parture? I apprehend this question has not 
yet been determined: Mr. Davy informs us 
(Researches, page 381,) that venous blood, 
agitated with atmospheric air and oxygenous 
gas, assumed the vermillion colour at its sur- 
face ; “but no perceptible absorption had taken 
place.” —Here then we have a change of co- 
lour without sensible absorption when the 
blood is in contact with the gas; is it pro- 
bable then that an absorption will take place 
when the blood is separated from the gas by 
a membrane of considerable thickness ? 
