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After 7 days the crust and the vesicular ring will be seen to have ex- 
tended somewhat, but the former has encroached more or less upon the 
area occupied by the latter. The subcutaneous cedema is less marked. 
After 8 days the lateral excursion of the lesion has definitely ceased 
and involution begins. This process of involution is evidenced by the 
spreading of the crust so that it finally occupies all the territory held by 
the vesicular ring. At the same time the zone of hyperemia fades the 
subcutaneous cedema disappears, and the lesions eventually consist of a 
crust of variable thickness, beneath which the normal epithelium is slowly 
spreading. If a few days later the crust be forcibly removed, either a 
small pocket of pus or a tough mass, adherent to the crust, will be found 
beneath, bordered by pink, new-formed epithelium which is growing in 
from the periphery. In some lesions the microscopic characters of the 
process are reflected in the appearances as presented to the naked eye to 
a greater extent than in others. Thus, in the vesicular ring two zones 
can at times be made out, an inner, opaque one and an outer, translucent - 
zone. ‘This agrees with the microscopic findings in some lesions where 
the leucocytes are seen beneath and to one side of the crust, while there is 
only clear serum in the peripheral part of the vesicle. 
Departures from the type lesion were seen in certain of our animals. 
In some cases the vesicle ring does not completely form around the crust, 
so that at the height of the process the crust may be bordered in part by 
elevated and hyperemic skin. In other lesions a vesicle may not at 
any time become recognizable to the naked eye. A variation which is 
not uncommon is for the lesion to undergo typical evolution, but for the 
different phases to be more or less delayed or accelerated. For example, a 
vesicular ring may be distinguished after 3 days or it may not be evident 
until after 6 days. In some lesions the process appears to start from 
a number of separate points instead of spreading symmetrically from the 
scratch. 
The typical process is considerably modified by the character of the 
skin at the site of inoculation. Thus, on the thick and hairy skin of the 
back the several zones of the lesion, which are clear enough in an inocula- 
tion on the abdomen, are not distinguishable. The same phenomenon is 
seen when the skin of the tail is inoculated. 
(b) The occurrence and macroscopic appearance of the exanthem.—In 
65 monkeys inoculated on the skin of the abdomen with variola virus, 
in one form or another, a general exanthem was noted in 50 (77 per 
cent). In the animals in which vesicle contents was used for inoculation 
the exanthem occurred in 32 out of 40 (80 per cent). The exanthem 
was first noted on the seventh day of the disease in 7 animals, on the 
eighth day in 26, on the ninth day in 14, and on the tenth day in 3. 
When vesicle contents was used for the inoculation, the exanthem was 
first noted on the seventh day of the disease 5 times, on the eight day 18 
times, on the ninth day 8 times, and on the tenth day once. 
