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not so great as in vaccination of the cornea. When pyogenic infection 
does not complicate the process there is no opacity of the cornea or con- 
junctivitis, and the lesions heal after a variable period. In 2 animals, 
which were allowed to survive long enough for the eruption to appear, an 
exanthem was seen on the sixth and seventh days of the disease. The 
evolution and extent of the exanthem was like that following the skin 
inoculation. Another animal, kept under observation for a long period, 
did not develop an exanthem. 
Histological examination shows that the process at the site of inocula- 
tion with variola virus on the cornea of the monkey consists primarily 
in degeneration and in proliferation of the epithelial cells. Seventy- 
two hours after the inoculation when the process is at its height the 
line of inoculation is marked by a defect in the epithelium, below which 
there may be a slight destruction of the corneal substance. The epithelial 
cells about this defect may be swollen and separated one from another, 
and show various degrees of degeneration. As we pass from the center 
of the lesion toward the periphery we find the epithelium much thick- 
ened. This increase in the thickness is in part due to swelling of the 
individual cells, shown particularly by those of the lower layer, which 
appear pale and assume a cuboidal or cylindrical form, and in part 
to an increase in the number of cells. At the point of greatest thickening 
the epithelium may measure twice its normal depth. In lesions of 
greater duration the degeneration of the individual cells and collection 
of fluid between the cells may occasionally result in the formation of 
minute cavities in the thickened epithelium, which are analogous to the 
vesicle of the specific skin lesion. 
Polynuclear leucocytes do not form a prominent feature of the corneal 
lesions. In many sections a prolonged search is necessary to find a single 
cell of this type. When the inoculation wound penetrates the corneal 
substance polynuclear leucocytes are more numerous. The paucity of 
these cells in the lesion is in strong contrast with the condition in the 
cutaneous smallpox lesions in the monkey. 
Cytoryctes variole were present in all the lesions examined. Their 
morphology and staining reactions were identical with those found in 
the skin lesions. No nuclear phases were present. The parasites were 
found as early as 18 hours after the inoculation and persisted through 
the eleventh day, that date being the last on which a microscopic 
examination was made. 
DISCUSSION. 
When we compare the lesion produced on the cornea of the monkey 
by inoculation with variola virus with vaccinial keratitis in the same 
animal we see at once that we have to do with a similar process. The 
only striking difference which these two lesions present is that in the 
variolous keratitis there is less exudation and the epithelium of the lesion 
does not become detached and cause a large superficial defect as in the 
