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Dr. Davy on 
substance of the lung generally, was in the same state ; and, 
besides containing a very few minute tubercles, it exhibited 
no other marks of disease. 
In the fatal case of Iredill, described in my former paper, 
pneumato-thorax took place in consequence of ulceration 
effecting a communication between the cavity of the pleura 
and a vomica in the lung. In this instance the disease origi- 
nated without the intervention of a vomica, and probably 
without ulceration ; it appears to have resulted from a com- 
munication between the aspera arteria and cavity of the 
pleura, established by the rupture of a superficial bronchial 
tube, and the membrane of the pleura covering it. It is sur- 
prising that accidents of this kind do not more frequently 
occur, considering the very large number of bronchial tubes 
that lie immediately under the pleural covering of the lung, 
and how delicate this membrane is, and how easily both it 
and the bronchia are torn. 
In a professional point of view, it would be an interesting, 
though not an easy task, to trace the different steps of the 
disease, of which I have given a brief history, from its com- 
mencement to its termination, and connect the symptoms 
with the organic changes that occurred. As more appropriate 
to this place, I shall confine the few remarks I have farther to 
make, to the air procured from the pleura. The following 
table exhibits, at one view, the composition of the air col- 
lected from the chest at different times. 
