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77
Small-Pox mortality in the first quarter of the present century
affords substantial evidence in favour of the protective influence
of vaccination.
It has been urged that the decline was too great to have
been due to the amount of vaccination which prevailed. It has
been shown, however, that the amount which was carried out was
very considerable, and the argument that such an amount was
insufficient to produce the decline in question is based on the
premiss that such an amount of vaccination would at the present
day be considered wholly insufficient protection. But it must be
borne in mind that in the countries so often mentioned a large
proportion of the population were protected by previous attacks
of Small-Pox, either natural or inoculated ; only a portion of the
population needed the protection claimed for vaccination. And
if the vaccination in the early years of the century was as general
as we have seen reason to think it was, that, added to the
protection afforded by previous attacks of Small-Pox, may be
regarded as adequate to have produced the decline in question.
Of course, as years went on, the proportion of the population
immune through previous Small-Pox became, owing to the
mere decline of Small-Pox, continually less and less, as the large
number who had had the Small-Pox in the previous century
gradually died out. After the first quarter of the century, that
part of the population which depended for immunity on vaccination
alone, became, in the absence of serious epidemics, greater
and greater; and an amount of vaccination adequate to afford
great protection in the earlier years ceased to be adequate for the
latter years. But this brings us to the periods succeeding the
first quarter of the century, which will be considered hereafter.
We have dealt thus with the evidence afforded by the first
quarter of the present century, because it constituted a convenient
epoch for inquiring whether mortality from Small-Pox had shown
signs of diminution in the period immediately succeeding the
introduction of vaccination, and not because the close of that