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14
III. That such articles become infective through contamination
from contact with sewage or sewagepolluted
water.
These conclusions furnish us with a definite basis of
enquiry. The question of infection by personal contact
having been disposed of, the ground is cleared for an
examination into the subject of contamination of food and
water. The first question suggesting itself is, does contamination
take place at a single source, or are the sources
multiple? In other words, is the food contaminated at a
central place, and afterwards distributed to the houses: or
is it contaminated at the houses themselves.
Difficulties lie in the way of the acceptance of any theory
of multiple contamination. No condition of any of the
houses was discovered capable of constituting itself a
general infecting agency. Nor was it likely that infection
was introduced through the water supply or by the drain.
The householders drew water from separate mains and
cisterns, and disposed of sewage into separate channels.
Indeed, the whole aspect of the outbreak, the sudden
appearance in rapid succession of a number of solitary,
widely distributed and apparently unconnected cases
in a district previously exempt, was opposed to such a
theory.
If, then, the theory of multiple contamination be dismissed
as untenable, the alternative argument holds. We conclude
that contaminated food had been supplied to the households
involved in the outbreak, from a central place where some
infecting agency is at work.
We now ask ourselves the question—among the articles
of food usually consumed in the ordinary household,
which lends itself most readily to the carriage of infection ?
And looking down the list, we do not find any other than