John Brownlee 
317 
increases ; that this is not due merely to the fact that larger marks are now put 
on than were formerly is shown moderately conclusively when it is considered 
further in detail. The degree of foveation of a cicatrix has been regarded as an 
indication of its protective value. Foveation, as a result of vaccination, no 
TABLE III. 
Mean Age of Persons with one Scar of different sizes, Glasgow 
1901, 1902, and 1904-. 
1901 
Size of Scar Foveated Not Foveated 1902* 1904 
0— -25 sq. in. 32-7 33-7 38-3 37-3 
•25— -5 „ 31-6 32-1 34-8 33-3 
•5—1 „ 28^1 29^3 33^4 32^0 
1— „ 26-1 27^5 28^3 32-9 
physician can foretell. The number, and, to a certain extent, the size of the 
cicatrices, is iu the hands of the operator, but as to whether the scar will turn 
out to be foveated or not depends upon a number of factors beyond his control, 
and yet the mean age of those with unfoveated scars is for each group higher 
than that of those in which the scars are foveated. This relationship also applies 
uniformly as far as I have been able to observe, and in the large epidemics where 
there is a sufficient number of cases to allow of finer gradation the same relation- 
ship holds. For instance, taking those cases in the epidemic in London in 1902 
in which there are four cicatrices of collective area greater than ^ square inch it is 
found that among those in which more than half of this area is foveated the 
mean age is lower than that of those in whom less than half is foveated, and that 
the mean age of the latter is in defect of that of those patients iu whom there is 
no foveation, the cicatrix being glazed or puckered. I do not think that this can 
be explained as may be suggested on the ground that foveation is a feature of the 
scar which tends to disappear with age, for it must be noted that the relationship 
just described bears a constantly present inverse proportion to that observed to 
exist between the same subdivisions and the mortality : that is to say, many 
marks are a better protection against death than few, larger than smaller, and 
foveated than non-foveated, and this to a greater extent than the mere difference 
of age incidence would imply. 
The susceptibility to smallpox of those with different numbers of marks is 
unfortunately a matter which cannot be determined directly, and consequently its 
full significance cannot be expressed in figures. It however can be investigated 
for London to a certain extent. At intervals of ten years since 1870 large out- 
breaks of smallpox have occurred in London. The number of persons affected at 
each age period with the number of their vaccinal scars is therefore known at 
four epochs separated by almost equal intervals of time, and consequently the way 
* The incidence of mean age is here due to the fact that the revacciuation in 1901 was performed 
more largely in the earlier than in the later ages. 
