go6 Dr. Davy's observations and experiments 
be not in the left pleura, but in a cavity of the mediastinum 
communicating with the right pleura, and containing a lobule 
of the right lung, dextri pulmonis additamentum , as Haller calls 
it, who has noticed this structure in the mediastinum of the 
dog and many other animals, and pointed it out as one of the 
principal causes of the erroneous notion that he combated.* 
Was the azote derived from the blood as an exhalation or 
secretion ? 
Facts might be advanced in favour of this idea. An exha- 
lation, or disengagement of azote appears to have taken place 
in the experiment of Messrs. Allen and Pepys, when oxygene 
nearly pure was respired.-f In the inspection of dead bodies, 
air has frequently been found in the vessels and closed 
cavities, which is probably azote.£ It has been asserted 
* Haller’s Opuscula Anatomica, p. 44. f Phil. Trans. 1809. 
J Vide Morgagni De sed. et Causis Morb. Epist. v. and Transactions of a So- 
ciety for the Improvement of Med. and Chir. Knowledge, vol. i. in which an inte- 
resting “ case of Emphysema not proceeding from local injury,” with some impor- 
tant observations relative to the secretion of air, is given by Dr. Baillie. 
Notwithstanding the experiments detailed by SirEvERAUD Home, in his Croonian 
Lecture, published in the Phil. Trans, for 1818, I am induced to believe that the gas 
in question is azote, rather than carbonic acid ; because the alkali in the blood is 
not saturated with carbonic acid ; because the serum of blood is capable of absorb- 
ing carbonic acid gas, rather more even than water, as I have ascertained by experi- 
ment ; because, during the coagulation of blood spontaneously, and the coagulation 
of serum by heat, 1 have never observed carbonic acid gas to be disengaged, when 
the experiments were properly made in vessels to which air could not have access, as 
in tubes completely filled with blood or serum, and inverted in blood or mercury ; 
and lastly, because I have not been able to procure carbonic acid gas from blood 
just drawn from the vessels, and still warm, when placed under a receiver, and com- 
pletely exhausted of air. I may here remark, that I have made two experiments on 
blood in vacuo, and in both with the same negative results. In one instance the 
arterial blood of an ox was employed, and in the other the blood of a man in health. 
In the former eight ounces were used, in the latter one ounce. In both instances 
