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59
Dilution of Polluting Matter.
The Royal Commission has evidently been much impressed
by the dilution to which any excremental matter must be
subjected in the rivers. Taking the smallest annual flow in the
Thames over Teddington weir in any one year, from 1881-91,
and the largest number of cases of enteric fever in any one
of those years, they show that this would give 294 million
gallons to one case. But as Mr. Murphy says, the risks to
London water supplies are less from the average number of
cases of enteric fever in the water area in a year than from
the occurrence of a number of cases at one time in a
community discharging its sewage into the river. Typhoid is
not distributed equally throughout the year, and regard must
always be had to the possibility of some exceptional outbreak—
due to milk, for example—giving rise to hundreds of cases of
the malady in towns situated a limited number of miles above
the intake, and discharging their sewage into the rivers ; for
there has been experience of a town having to discharge its
sewage, untreated into the river owing to the temporary failure
in its machinery for treatment, and this at a time when the
town was suffering from an epidemic of enteric fever.
Comparison Between Wells and Rivers.
The Royal Commission would appear to admit that, in the
case of the Caterham Well, the typhoid poison was waterborne ;
but, appealing to the arithmetical test of dilution, they maintain
that no argument derived from that case can be applied to a
river, in which the volume of water is so much greater. But
Mr. Murphy shows that we have no accurate knowledge of the
amount of water which a single case can render virulent, and
that certainly no safe deduction of this kind can be made from
the occurrence at Caterham; for the man who there gave rise
to the infection was only employed in the well during a portion
of the day, and in his evidence he insisted that, when in the
well, he always used the bucket, and that his evacuations were
sent to the surface. The contamination may therefore have