J. R. ALLEN, J. M. JENNY AND C. F. CHESNEY 
189 
Figure 2. — Hypertrophy of smooth muscle cells in the 
wall of a small muscular artery is depicted (arrow). 
Loss of the muscular components and replacement 
by hyaline material is shown in closely associated ar- 
teriole and muscular artery. H & E stain ; x 413. 
Figure 4. — Thrombi developed in the lumens of large 
pulmonary arteries of 5 animals. Note the predomi- 
nantly fibrinous nature of the thrombus. The entire 
vessel wall is edematous and numerous leukocytes 
are obvious throughout. H & E stain; x 45. 
phological alterations in the vessel walls. In 
many of the small muscular arteries, occlusion 
was attributed to the extensive hypertrophy of 
the endothelial and smooth muscle cells (Figure 
2). These cellular modifications resulted in re- 
duction or obliteration of the lumens of the af- 
fected arteries. Other arteries had obvious rents 
in their endothelium. Blood cells and plasma ac- 
cumulated beneath these injured areas leading 
to further disruption of the vessel wall. There 
Figure 3. — Extensive intimal disruption is depicted in 
this medium sized pulmonary artery. Notice the dis- 
tance between the internal elastic lamina and remains 
of endothelium. Edematous disruption is also appar- 
ent in the medial portion of the wall. Mononuclear 
cells are prevalent between the fibrous strands of the 
adventitia. H & E stain; x 158. 
were also other arteries whose walls and lumen 
were partially or completely replaced by hyaline 
material (Figure 2). Electron microscopically, 
these vessel walls were composed primarily of 
amorphous and fine fibrillar material similar to 
basal lamina. 
In the larger arteries there were breaks in 
the endothelial lining and intimal disruption 
produced by the extravasated blood (Figure 3) . 
In the more severely affected vessels, erythro- 
cytes, leukocytes, and plasma were also present 
between the muscular components of the media 
and adventitia. In many instances, fibrin and 
platelet thrombi developed in areas of the vessel 
having a disrupted endothelial surface (Fig- 
ure 4). 
In close association with the disrupted capil- 
laries, arterioles, and arteries were thickened 
alveolar walls consisting of fibrous connective 
tissue, macrophages, and histiocytes. In well de- 
marcated areas of the lungs of 4 animals, there 
was epithelialization of the alveolar lining cells. 
These closely associated large columnar cells 
contained centrally located nuclei and numerous 
cytoplasmic organelles. 
The myocardium of the left ventricle had en- 
larged muscle cells, but appeared normal other- 
wise. The edematous right ventricular muscula- 
ture of all the infants was characterized by 
widely separated myofibrils, numerous areas of 
organelle-free matrix and numerous variable- 
