d01 
the immunity. The brief evolution and abortive development of the 
lesion of the exanthem is what might be expected in an animal which 
had already developed such a germicidal power in its plasma that its 
presence in the inoculation wound, and in the subsequent exudate stream 
of inflammatory origin, inactivated the virus introduced at the site of a 
skin inoculation. 
In the lesion developing spontaneously on the skin, the immune plasma 
doubtless does not have as free access to the organisms as is the case where 
the virus is mixed in a scratch with fresh drawn blood serum. 
The phenomenon of an exanthem in variola inoculata and its absence 
in vaccinia is not explained by these experiments. Had it proved that 
the general immunity was of notably later development in variola inoc- 
ulata the exanthem producing quality of variola virus would readily 
have been explained. However, the reverse seems to be the case, and 
we have to seek further for the explanation of this fundamental dif- 
ference between the two viruses. 
Simultaneous variolation and vaccination of the monkey shows that 
the synchronous development of a vaccine lesion has no effect upon the 
appearance of the exanthem of variola inoculata. The fact that vaccina- 
tion on or about the date of exposure to smallpox inhibits the produc- 
tion of clinical types of variola vera, characterized by an exanthem, 
emphasizes the difference between the diseases variola vera of man and 
variola inoculata of monkeys. 
In a previous section we have shown that the immunity potential of 
the mucous membrane is low. In variola vera it seems exceedingly prob- 
able that the atrium of infection and the site of the primary lesion is on 
a mucous membrane. If such be the case we would expect that little if 
any immunity would develop as a result of the evolution of this lesion, 
and the organisms which seek the skin to produce the exanthem would de- 
velop in a practically nonimmunized animal. This agrees with the course 
of the exanthem in a typical variola vera in man. In other cases of small- 
pox the exanthem shows an evolution very like that in variola inoculata 
(variola abortiva), or is absent (variola sine exanthem), and in these we 
conceive the organisms which go to form the exanthem as acting against 
a more or less fully developed immunity. This condition might be 
dependent upon an early development of the general immunity arising 
from the primary pock, and be conditioned by its locus. In any ease, 
a vaccination on the skin at the time of exposure produces an immunity 
which develops before the exanthem, probably killing the organisms in 
transit from the protopustule to the skin, and so inhibiting the eruption. 
This suggests an explanation of the failure of all attempts to abort 
the exanthem in variola vera by the injection of what certainly were 
highly germicidal sera (Béclére and others). 
It is evident that at the time when the case is fully declared to be 
smallpox and is put under treatment, the organisms are inaccessible 
