330 
Smallpox and Vaccmation 
excess of what might be expected as to make it probable that these figures are 
not sufficiently large to be taken as trustworthy. The actual protection, however, 
which one attack of smallpox affords against a second is much larger than that 
conferred by vaccination ; this protection, judging from the Sheffield census, is 
very high, the correlation coefficient being "6, and this high correlation of protec- 
tion against attack suggests the probability of some eri'or in the death rate as 
given above. 
The protection given by revaccination is still higher than that given by a 
previous attack of smallpox and by recent revaccination practically absolute. Of 
the 400,000 persons revaccinated in Glasgow in 1901 six were admitted during 
the epidemic of 1904; three of these stated that there had been no local reaction, 
they were therefore not effectively revaccinated ; one stated that there had been a 
local reaction, which, however, left no scar. In the other two the condition of the 
arm indicated successful revaccination. That is out of 400,000 persons three at 
the most were affected with smallpox after a lapse of three years, while of the 
other 250,000 inhabitants of Glasgow more than 800 succumbed. In the statistics 
published in the London epidemic of 1902 the mean period which has elapsed 
between revaccination and the attack of smallpox (23"9 years) falls considerably 
short of the mean age of those attacked by smallpox in the same epidemic 
(28'6 years) with the protection alone of infantile vaccination. These persons, 
however, must represent a more susceptible class, for, judging from the Shefifield 
epidemic, the correlation between the revaccinated who escape and those who 
were attacked and the like classes of the vaccinated is very considerably in favour 
of the former. 
TABLE XVL 
Table of Revaccinated Persons Attacked by Smallpox. London, 1902. 
Age at Attack. 
as 
> 
CD 
0) 
bX) 
<1 
I 
1 
1 
o 
so 
1 
1 
1 
1 
1 
o 
1 
*o 
1 
o 
^2 
1 
Totals 
'J; 
so 
''O 
0— 5 
5—10 
1 
1 
1 
1 
4 
1 
9 
10—15 
1 
2 
5 
2 
4 
7 
5 
1 
27 
15—20 
1 
6 
2 
10 
3 
2 
2 
1 
27 
20—25 
1 
2 
5 
1 
2 
1 
12 
25—30 
1 
1 
2 
1 
5 
30—35 
1 
3 
2 
1 
7 
35—40 
1 
1 
40-45 
1 
1 
45—50 
1 
1 
50—55 
1 
1 
55—60 
60 65 
1 
1 
Totals 
2 
3 
6 
11 
9 
24 
18 
10 
4 
1 
3 
1 
92 
