6o Sir Everard Home’s examination into the 
Surgeon. To him I am indebted for having taken the trouble 
of making injections of the arteries, the veins, and of the cells 
of the lungs, with different substances, so as to enable Mr. 
Bauer to expose and examine them on the field of the 
microscope. 
The first new fact discovered in the course of this enquiry 
was, that although the common minute injection used by 
anatomists for filling the blood vessels, when thrown in by 
the trunk of the pulmonary artery, while the cells of the 
lungs are empty, returns again by the trunks of the pulmo- 
nary veins, yet when thrown in by the veins, it is not 
returned by the trunks of the arteries. 
Another fact was discovered ; that during the momentary 
distention of the air cells, an interruption is produced between 
the arterial and venal circulation in the lungs, the blood being 
carried no farther than the small arterial branches surround- 
ing the air cells. 
The following description of the air cells, and the parts 
surrounding them, is taken from the annexed microscopical 
drawings of Mr. Bauer. 
As accurate representation surpasses all verbal description, 
I shall not have occasion to do more, to make myself under- 
stood, than to mention the parts themselves, and the circum- 
stances under which they are represented. 
The cells of the lungs were filled with quicksilver, to show 
their utmost capacity, and the parts were afterwards immersed 
in rectified spirit, to prevent the cells from collapsing, when 
the quicksilver was allowed to escape. 
When the internal cavity of a single cell was exposed, 
immediately behind its internal membrane, the branches of 
