(en eae ee | 
323 
It seems evident that the immunity which the animal presents to the 
skin inoculation must depend upon certain properties of the individual 
conferred upon it by. the disease which follows the first inoculation. The 
weight of evidence is in favor of the immunity being due to a bactericidal 
or germicidal property resident in the blood serum (Sternberg and Reed, 
Béclére, Chambon, and Menard). If such be the case the animals in 
which complete immunity to vaccinia follows variolation, and in which 
complete immunity to variolation follows vaccination, indicate that the 
immune property of the serum of the inoculated animal, whether vaccina- 
tion or variolation be practiced, is identical. We then would expect to 
find simply a quantitative difference in this germicidal property of the 
sera of the animals, depending upon the character of the virus used for 
inoculation. The reason that variola inoculata always protects against 
an inoculation with variola virus, if confirmed by more experimental 
evidence than we present, would be that the variola virus is less potent 
upon the monkey than vaccinia virus, in that it fails to develop in 
monkeys protected by previous variolation, whereas the latter develops 
and produces a lesion. 
That the immunity resulting from inoculation of the monkey with 
variola virus is less efficient than that resulting from vaccination is 
apparent from the fact that vaccination protects against both subsequent 
variolation and vaccination, while variolation protects against subsequent 
variolation and only partially against subsequent vaccination. 
At the present time technical difficulties prevent the putting of the 
quantitative aspects of the above hypotheses to the test of experiment. 
CONCLUSIONS. 
(1) A vaccine lesion on the skin of the monkey (M. cynomologus) 
confers upon the animal an immunity to subsequent inoculation of the 
skin with vaccine or with variola virus. 
(2) A variolous lesion on the skin of the monkey (JM. cynomologus) 
protects the animal against subsequent inoculation of the skin with 
variola virus, but does not in all cases protect against later inoculation 
with vaccine virus. 
(3) The failure of variola inoculata in the monkey to protect against 
subsequent skin inoculation with vaccine virus depends upon the fact 
that this species of animal produces a smaller amount of the germicidal 
substance necessary to inhibit a second inoculation after variolation than 
it does after vaccination. 
4 
2. ON THE INFLUENCE OF THE LOCUS OF INOCULATION UPON THE DEVELOP- 
MENT OF THE IMMUNITY IN VARIOLA AND VACCINIA IN THE MONKEY 
(MACACUS CYNOMOLOGUS). 
Introduction.—In the preceding section we have studied the immunity 
reactions of the monkey to inoculation of the skin with variola and with 
vaccine virus and have brought out certain differences in the immunity 
897148 
