SECT. XVI. PHYSIOLOGY. 127 
the pulmonary and costal pleura. The contractile 
force of the lungs, in these cases, must have been 
superior to the weight of the atmosphere; which 
I should feel much disposed to disbelieve, did it 
not rest on such high authority. 
cecr. On opening the chests of animals, whe- 
ther dead or alive, I have always found the 
pulmonary and costal pleura in contact, except 
when separated by air or fluid. But Bichat, after 
asserting the existence of a vacuum between 
them, argues thus: “ if the lung collapsed in the 
body at the instant of opening the chest, it would 
be from the pressure of the external atmosphere, 
a pressure which would expel the air contained in 
this organ, through the trachea; or if, to stop the 
egress of this fluid, you shut this canal herme- 
tically, by fixing a tube to it with a closed cock, 
and afterwards let the chest be opened, the lung 
equally collapses; then the air had previously 
escaped. Make, on the contrary, the same expe- 
riment on a living animal, and you will always 
prevent the collapse of this organ, by preventing 
the escape of the air.” These experiments seem 
to be recorded with all the candour of their great 
author; but to me, I confess, they appear inex- 
plicable by the cooling of the air after death, 
unless the trachea were hermetically closed at 
that period. For further information on Bichat’s 
theory, see his work, Sur la Vie et la Mort, 193. 
