AIR SPACES IN LUNG OF CAT 475 
Surely this is not dichotomy; neither is it trichotomy, although 
in one division it is the type and partially prevails in two others. 
It seems to me that, in a certain degree, it conforms to the state- 
ment of Flint that there may be alternation of the two processes, 
dichotomy and monopody. 
ALVEOLAR PORES 
A distinction must be made between the wide open communica- 
tions of the older authors and the perforations which were first 
described by Adriani as occurring here and there in the walls of 
the alveoli, by means of which adjoining alveoli were in communi- 
cation with each other; the so called alveolar pores. In 1892 I 
called attention to these openings, quoting Henle’s statement 
that he did not consider them normal structures, but rather the 
result of atrophy and resorption of the lung tissue. In 1893 
Kohn brought these structures. prominently into notice by de- 
scribing openings in the alveolar septa through which, in cases of 
pneumonia, fibrils of fibrin, could be traced from one sacculus 
alveolaris to another. He did not consider these openings to be 
normal, but rather the result of the pathological process. 
The investigations of Ribbert, Hauser, Herbig and Bizzola on 
the side of pathology; of Aigner, von Ebner, Laguesse, Oppel and 
myself on the side of normal histology and of Flint on that of 
embryology lead to the same conclusion. On the other hand, 
Hansemann, Zimmermann, Merkel, Schulze and Marchand be- 
lieve that they are normal structures. 
It seems to me that history is repeating itself in this discussion 
as to the presence or absence of pores in the alveolar septa. In 
the present instance we have ‘pores,’ while in the earlier it was 
‘stomata.’ The same factors which are capable of producing ° 
the well known artifacts, stomata, can produce these openings; 
that is, anything causing separation of the epithelial cells or 
rupture of the delicate frame work of the septa, as for example 
over distention, inflammation, desquamation of the epithelium, 
atrophy and age. The recent investigations of Walter show very 
JOURNAL OF MORPHOLOGY, VOL. 24, No. 4 
