285 
Animal killed and autopsy done at once. Material saved for histological ex- 
amination of specific lesions and of the viscera. Axillary lymph nodes enlarged 
and red. On section much blood-stained fluid exudes from the cut surface. 
Il. Histological examination. 
The primary lesion 18 hours after inoculation: Microscopic examination of 
sections from the site of the inoculation shows a solution of continuity which 
involves the epithelium and may or may not extend into the corium beneath. 
The defect is filled by an exudate composed of polynuclear leucocytes which lie in 
a meshwork of fibrin. On the surface the elements of this exudate are fused 
into a crust. On either side of the defect the epithelial cells of the rete are more 
or less swollen, and some present clear, circular areas in their protoplasm, sug- 
gesting hydropic degeneration. The nuclei of these cells are swollen and the chro- 
matin tends to collect in masses. Polynuclear leucocytes are present in consider- 
able numbers in and around the vessels of the corium and in the connective fissue 
beneath the defect. The leucocytes are streaming into the defect and into the 
adjacent epithelium. 
Forty-eight hours. ‘The sections present the same general characters as those 
from the earlier lesions. The defect in the epithelium is sometimes obliterated 
in such a manner that a layer of epithelium is interposed between the exudate 
which has collected beneath the crust and the injury to the corium. The poly- 
nuclear leucocyte infiltration is more intense. The epithelial cells of the lower 
layers of the epidermis about the line of inoculation show more marked degenera- 
tion, and the cells are frequently separated one from another by fluid. 
Three days. The crust has increased in thickness and, with the destruction of 
the epithelial cells in the central line of the lesion, may fuse with the corium. 
The epithelial cells of the lower layers adjacent to the crust show various forms 
of degeneration. Some present ballooning degeneration, and the accumulation of 
fluid between the cells is more evident than in the earlier lesions. In places, 
vesicle formation is foreshadowed by the appearance of small, irregular cavities 
formed either by the accumulation of fluid between the cells or by the bursting of 
hydropic cells. The corium is the site of a definite reaction, shown by an enlarge- 
ment of the endothelial cells of the blood and lymph vessels. These enlarged 
endothelial cells may contain cytoryctes. There is a marked polynuclear leu- 
cocyte infiltration of the corium and the epithelium about the crust. In some 
cases a mass of leucocytes, with granular precipitate and fibrin, is found in the 
corium just beneath the center of the lesion. The cellular sheaths of the hair 
follicles show changes similar to those seen in the cells about the crust, and an 
abundant polymorphonuclear infiltration is present. Some lesions of this age show 
definite vesicle formation such as will be described later. 
Four days. Lesions of this age may present vesicular cavities under the lateral 
expansions of the crust. In some lesions the whole crust is elevated and the 
lateral vesicles communicate with one another. The epithelium at the sides of 
the lesion and below the lateral portions of the vesicle is more or less swollen 
and shows various degenerations, the most marked forms of which are found in 
those cells nearest the center of the lesion. The epithelium is completely de- 
stroyed in the axis of the lesion. The corium beneath shows proliferation of the 
endothelial cells of the blood vessels and of the lymphatics, together with an 
enlargement of the connective-tissue cells. A polymorphonuclear leucocyte infil- 
tration is apparent in the corium and in the thickened epithelium about the vesicle. 
In some lesions the contents of the vesicle shows a predominance of polymorphonu- 
clear leucocytes under the crust, while the outer portions are all but free from 
these cells, containing only granular precipitate and fibrin. 
Five days. The topography of the lesion at this stage shows considerable 
variation, due to differences in the extent of the vesicle formation. The typical 
