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117
small per centage. A broad margin might be allowed for error
without the force of the argument derived from the contrast being
seriously diminished.
The next point for consideration is the question whether the
evidence shows that vaccination has a protective effect against an
attack of Small-Pox. We have lately been considering whether
it affords any protection against death from the disease in persons
attacked by it. The question with which we have now to deal
obviously presents greater difficulty in arriving at accurate results.
The liability to attack depends on contact with or proximity to
sources of infection. When an epidemic of Small-Pox visits a
town, the liability to infection of the inhabitants of different parts
of the town may differ widely. Those who are residing in a house
where a person is suffering from Small-Pox are subject to a risk
which does not attach to persons living in a house not so invaded.
On the other hand, persons moving about the town, or congregating
for purposes of business or pleasure may come in contact
with sources of contagion, so that the risk of contagion is, of
course, not confined to those who are living in a house where
Small-Pox is present, though it may be greater in the case of this
class than of the rest of the community. These considerations
appear to have been kept in view by the medical men who have
dealt with the matter in their reports on the local epidemics to
which we have so often referred.
In his report upon the outbreaks in London during 1892 and
1893 Dr. Luff has not entered into the question of the rate of
attack among the unvaccinated as compared with the vaccinated.
His report, nevertheless, affords some data for such a comparison.
Of a total number of 2,353 cases as to which he obtained information
there were 409 unvaccinated persons, or 17.3 per cent. It is
not likely that the percentage of unvaccinated persons, whether in
London or in the districts specially effected, was as great as this.
Dealing with the age period 0—10, there were 358 attacks.