on air found in the pleura, &c. 501 
and thus tends to account for the accumulation of the latter 
gas in the preceding case. 
It may be said, that the experiment does not warrant the 
inference that any azote was absorbed, and, consequently, 
that the expression “ in a greater proportion/’ is incorrect. 
The absorption of this gas is probable, however, though not 
demonstrated in the present instance, as Sir Astley Cooper 
has found that common air introduced into the cellular mem- 
brane, and into the cavity of the thorax and abdomen of 
dogs, is, after a certain time, entirely removed by absorption.* 
Relative to the source of the carbonic acid gas, it is easy to 
conceive that it was formed, or emitted, in the air cells of the 
lungs, as in ordinary respiration ; and that, mixing with the 
air inspired, it was received into the pleura. If thus derived, 
and not from the surface of the pleura by secretion, it seems 
to follow, that it is less readily absorbable by the pleura, than 
oxygene. To endeavour to decide this point, the following 
experiment was made. 
About 30 cubic inches of air, consisting of 80 parts com- 
mon air and 20 carbonic acid gas, were passed from a receiver 
into a bladder, furnished at one extremity with a stop- cock, 
and at the other with a small trochar ; both air tight. A 
small incision having been made through the integuments 
of the right side of the chest of a dog, the trochar was passed 
through the intercostal muscles into the pleura. The stil- 
lette was immediately drawn from the cannula into the 
bladder, and the air of the bladder instantly rushed into 
the pleura, and, on expiration, was in part forced back into 
* Surgical and Physiological Essays by John Abernethy, p. 55 ; London, 
> 793 * 
