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and years which were not epidemic, as in those of Geneva (1580—
1760), which show that the feature was apparent earlier than the
eighteenth century, in those of Sweden (1774—1800) and in those
of other places. Incidental references in various writings show
that the fact was recognised at the time; thus Haygarth observes
that in Chester in the years 1772—1777, of those under ten
years, 'half as many die of the Small.Pox as of all other
diseasesand this feature of Small.Pox is assumed in the
calculations of Bernoulli referred to above.
The first quarter of the 19th century was characterised in
this and other countries by a striking decrease of Small.Pox.
In the London Bills of Mortality the returns of Small-pox
for the year 1800 are 2,409. This was the last return so high as
2,000. From thence onward, the number of deaths from SmallPox
fell, especially after 1810, reaching in 1818 so low a figure as
421 ; the fall being irregular and marked by epidemics as in 1812,
1817, and 1825. This decline is all the more'striking since during
this period the population of London, within the limits of the
Bills, increased from 746,233 in 1801 to 1,180,292 in 1831. As
has been already urged the Bills were imperfect, and there is
ground for believing that during this quarter of the century the
imperfections were greater than in former times. This is confirmed
by the fact that the returns of the total deaths, in spite of
the increased population, were on the whole not greater, in many
years even less, than in the preceding century. Making evety
allowance for the effects of improved sanitary conditions, this
feature of the returns may be taken as evidence of their imperfection.
Still, in spite of their imperfect character, the Bills show
that during this quarter of the century, a striking change took
place in Small.Pox in London.
What was the cause, or what were the causes, of this marked
decline of Small.Pox in the first quarter of the nineteenth
century ? Was it due to the introduction of vaccination, or is it
to be otherwise explained ?