507 
on air found in the pleura, &c. 
lately, that air thus found is, in every instance, the conse- 
quence of putrefaction. But surely the accurate Morgagni 
was not so egregiously deceived. Many times I have 
noticed air in the Vessels of the pia mater, in bodies only a 
few hours dead, and very lately I detected some in the inter- 
nal jugular veins of a body that had been dead only eighteen 
hours, and free from every mark of incipient putrefaction : 
and I lay the more stress on this observation, because it was 
very carefully made before any large vessel was divided 
through which air could gain admission. Farther, air seems 
to pass pretty readily (probably through the exhalants) from 
the air cells of the lungs into the pleura. Is not this proved 
by an experiment of Hales ?* And an experiment which I 
have made, and which I may briefly notice, seems to afford 
some proof of it. Immediately after death, before the 
muscles had lost their irritability, I inflated the lungs of a dog 
under water by means of a double bellows, through the 
trachea. Air in exceedingly minute bubbles escaped from 
the surface of the pleura covering one of the inferior lobes ; 
and on making gentle pressure with the fingers on any part 
of the inflated viscus, the same appearance presented itself. 
These circumstances, which I have ventured to bring for- 
ward as somewhat favourable to the idea of the secretion or 
exhalation of azote, are still far from conclusive. After hav- 
ing given the subject all the attention in my power, I do not 
venture to draw a positive conclusion. I have thought it 
the blood remained perfectly tranquil, when the vacuum was as complete as coul^ 
be made with a good air pump, and of course did not exhibit the slightest traces of 
the disengagement of any air. 
* Vide Stat. Essays i. 252. 
