AIR SPACES IN LUNG OF CAT 465 
ULTIMATE ENDING OF THE BRONCHIAL TREE 
For an extended review of the older literature I will refer the 
reader to my previous contributions and to the excellent résumé 
by Oppel. 
In 1892 I published the first of a series of contributions on the 
finer structure of the lung which seem to have stimulated renewed 
interest in this complex organ. The introduction of Born’s 
method of reconstruction placed in the hands of the investigator 
a method by which the relation of the air spaces to each other 
and to the bronchial arborization as well as the form of each 
could be definitely determined. By means of this method, using 
the lung of the dog for my study, I made a reconstruction of all 
the air spaces connected with a bronchiolus respiratorius. 
By following a bronchus to its ultimate division we find that 
the smallest branches are no longer smooth but bear on their 
wall alveoli. The smallest division of the bronchial tree which 
has smooth walls I named in previous descriptions bronchus III 
(bronchiolus B. N. A.j}. The branches arising from the bron- 
chiolus, the bronchioli respiratorii, bear alveoli which increase in 
size and number towards their distal end. Each bronchiolus re- 
spiratorius branches, giving rise to the smallest divisions of the 
bronchial tree, the ductuli alveolares. The air spaces connected 
with a given ductulus alveolaris, together with that ductulus al- 
veolaris, form the lobule. 
With the lobule thus defined it is necessary to describe what 
is situated peripheral to the ductulus alveolaris. During the 
past twenty years I have made numerous reconstructions of the 
air spaces in the lungs of various animals, and I have found no 
occasion to modify my original description. 
Leading out of the distal extremity of the ductulus alveolaris are 
from three to six openings which are more or less circular in 
outline. These openings do not all take the same direction; 
usually one of them appears as though it were a continuation of 
the ductulus alveolaris, while the others open out at various 
angles or may take a course nearly recurrent to that of the duc- 
tulus alveolaris. These openings lead into the atria. Each at- 
