farther particulars of a case of pneumato-thorax . 263 
Composition. 
When collected. 
# 
Carbonic acid. 
Oxygene. 
Azote. 
May 21 
7 
. 
93 
July 15 
7.5 
2.5 
90 
— — — 20 
6 
5-5 
88.5 
— — 29 
8 
4 
88 
30 
16 
1-5 
82 .5 
To what are these variations in composition, which the 
table exhibits, owing ? I cannot conceive that they depend 
entirely on the admission of variable quantities of atmospheric 
air by the external opening, because exceedingly little at- 
mospheric air could enter through that channel, both from 
the great care taken to exclude it, and from the valvular 
nature of the passage.* I believe we must look chiefly to 
the source of the air and the absorbent power of the pleura 
for the explanation in question. In this case, as in Iredili/s, 
there is reason to suppose that the air accumulated in the 
chest was common air, more or less vitiated by respiration 
previously, and more or less altered by the process of absorp- 
tion after entering the cavity of the pleura. Taking this view 
of the subject, the composition of the air each time it was 
examined, is easily accounted for, excepting in the last in- 
stance, when the proportion of carbonic acid gas was found 
* The perforation being slightly oblique, the pleura costalis lined with coagu- 
lable lymph, closed the internal aperture in the rib on expiration, and prevented 
completely the egress of air, even when the dressings were removed, and the external 
aperture uncovered. When the trochar was introduced, the stilette was withdrawn 
during expiration, and the finger was applied to the mouth of the canula during 
each inspiration. 
