49 8 Dr. Davy's observations and experiments 
The right lung was carefully dissected out. In the upper 
part of its superior lobe “ a tubercular excavation,” or vomica, 
was found, of the capacity of about four ounce measures, 
which communicated with the aspera arteria by a large 
bronchial tube, the ulcerated end of which terminated in the 
side of the excavation opposite to the openings by which the 
vomica communicated with the pleura. 
On examining minutely the communication between the 
cavity of the chest and the lung, a kind of valvular structure 
was discovered, which would allow of air being pumped into 
the pleura in the act of inspiration, but not of its escape in 
expiration, owing to which, no doubt, the accumulation of air 
in question took place. Even at the risque of being tedious, 
I must attempt to convey some idea of this structure. Be- 
tween the false membrane of the vomica and the pleura there 
was a small irregular sinus, not exceeding an inch in diameter, 
the sides of which though not adhering, of course were in 
contact, or very nearly so. This sinus was the channel of 
communication, and contained the valvular structure alluded 
to. It opened into the cavity of the chest by a hole in the 
pleura pulmonalis about the size of a crow-quill, and into the 
vomica by three smaller holes in the substance of the lung, 
not corresponding with the former, so that a probe could not 
be passed from one into the other in a straight line ; and, con- 
sequently, when the surfaces of the sinus were pressed to- 
gether by the compression of the air in the pleura in the act 
of expiration, the communication through which the air 
entered was closed, and its exit prevented. 
I shall now proceed with the description of the remaining 
morbid appearances. Besides the vomica described in the right 
