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PULMONARY MODELS 
More isolated pieces of tissue are seen in thin, 
i.e., 1-4 u, sections of emphysematous lung than 
in thick, i.e., 100 u sections, both of which are 
commonly examined with a light microscope. 
The isolated pieces are not seen in the 2/mm 
slices used for sub-gross studies, or in SEM 
micrographs, because at least one end of most 
trabeculae are attached to the thick specimens 
(Figure 5). 
We saw scale-like plaques only in SEM micro- 
graphs of emphysematous lung lesions (Figures 
5, 6 and 7). These have heretofore not been 
described. Whereas we have had excellent cor- 
relation between cell types observed by trans- 
mission and SEM in studies of normal lung, we 
are to date unable to completely characterize the 
plaques. They have some of the characteristics 
of alveolar macrophages; it is also possible 
that they could represent desquamated type I 
or type II alveolar epithelial cells. Neither of 
these possibilities seem likely as we have not 
seen plaques in normal areas of the emphysema- 
tous horse lungs, in lungs from normal horses, 
or in lungs of other species of mammals. We are 
now examining emphysematous lung tissue 
from human beings to determine if plaques are 
present. 
SUMMARY 
Our studies in horses have shown that chronic 
obstructive lung disease has resulted in greater 
than normal pulmonary arterial pressure and 
Figure 5. — SEM of emphysematous horse lung. Cut 
edge of trabecula and interalveolar septum. A plaque 
is at the junction of the trabecula with the septa. 
Figure 6. — SEM of emphysematous horse lung. Plaque 
on the junction of anastomosing trabeculae. 
less than normal lung compliance and pulmo- 
nary diffusion capacity in the animals. The in- 
creased pulmonary resistance and impaired 
maximum expiratory flow rate at various lung 
volumes were characteristic of these animals as 
defined in initial studies. The electron micro- 
scopic studies have quantitatively shown de- 
crease in pulmonary capillaries per cm of al- 
veolar wall as well as other cell population 
changes in the emphysematous horse lung. Also, 
as indicated above, the most recent studies in- 
volving scanning electron micrographs of sec- i 
tions of emphysematous horse lungs have shown [ 
new "scale-like" visions not previously seen in j 
the emphysematous lungs. j 
„ 1 
Figure 7. — SEM of emphysematous horse lung. Plaque 
and type II alveolar epithelial cell on surface of 
trabeculae. 
