158 
MR. ADDISON ON THE AIR-CELLS OF THE LUNGS. 
Cruveilhier and Majendie, however, describe the air-cells as freely communica- 
ting- with each other, in the interior of each lobule ; but I am not aware that either 
of these authors has given any detailed or minute description of the aeriferous struc- 
ture of the lung*. 
Having been engaged in investigating by the microscope the seat and nature of 
tubercles in the lungs, and having examined the structure, recent and dry, in every 
possible way I could devise, I nevertheless always failed to discover any tubes ending 
in cuts de sac; on the contrary, I always saw air-cells communicating with each other 
in every section I made. 
I therefore repeated several of Reisseissen's experiments, and instituted others, 
from which I derived ample evidence that the bronchial tubes, after dividing into a 
multitude of minute branches which take their course in the cellular interstices of 
the lobules, terminate in their interior in branched air-passages, and freely communi- 
cating air-cells . 
In a foetal lung the bronchial ramifications in the interior of a lobule, or the intra- 
lobular ramifications have a regular branched arrangement, subdividing in all direc- 
tions, somewhat dichotomously, and terminating at the boundary of the lobule in 
closed extremities. It is not, however, at the boundary of the lobule only that these 
closed extremities or culs de sac terminations of the intralobular bronchial ramifica- 
tions are placed, many of them may be seen in the interior of a lobule, lying against 
and pressing upon the sides of the adjoining branches (a), Plate XII. fig. 8. 
It is important to remark, that there are no anastomoses to be seen between the in- 
tralobular bronchial branches ; each branch pursues its own independent course, 
until it terminates in a closed extremity. 
Anatomical writers generally use the terms air-vesicles and air-cells synonymously, 
so that they are convertible terms; but strictly speaking, an air-vesicle is an air- 
bubble, and may exist either in or out of a pulmonary air-cell. It is not necessary 
to the existence of an air-bubble, that it should be contained in a membranous enve- 
lope ; hundreds of them may not only exist, but in any slightly viscous liquid may 
even press against each other, without losing their figure or globular isolation. 
In a foetal lung neither air-bubbles nor air-cells exist; but when an animal respires, 
the entrance of the air into the lungs inflates all the lobules to twice or three times 
their foetal dimensions, and the intralobular bronchial ramifications experience a 
great and important change both in figure and character. The delicate membrane 
composing them opposes an unequal degree of resistance to the pressure of the air, 
which is very considerable, and it is consequently distended into little globular infla- 
tions, forming a series of communicating cells, which are immediately and perma- 
* Cruveilhier’s Anatomy, by A. Tweedie, M.D., F.R.S., p. 552. Majendie’s Lectures. 
t I have adopted the appropriate and now universally received terms of Mr. Kiernan, which exactly express 
a very necessary distinction between the bronchial ramifications in the cellular interstices of the lobules, which 
are always tubes, and those in the interior of the lobules, which are tubular only in the foetus. 
