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by comparing as far as possible the rates of incidence on rural districts supplied with Tees water, and
on rural districts otherwise supplied.
4. The absence of known occurrence of one or more cases of enteric fever between July 1st and
August 13th among the population draining into the Tees will not be regarded by medical men who
are familiar with " ambulatory typhoid" as any sufficient reason for assuming that the specific virus of
the disease had not had opportunity of finding its way into the river. The illness of the man who
polluted the Caterham well would never have been heard of but for the detailed inquiries to which the
outbreak in the Caterham valley gave rise.
After study of Dr. Barry's report and the evidence of Mr. Wilson, I have no hesitation in stating
that this evidence may be dismissed, as in no sense invalidating Dr. Barry's conclusions. His conclusions,
indeed, I am satisfied, must be accepted as certainly as the evidence concerning the Broad-street
well of 1854 and the Caterham well of 1875, evidence which the Royal Commission evidently accepts as
amounting to proof.*
Nor indeed do I regard Dr. Barry's conclusion as a startling hypothesis. The enormous power of
water to disseminate disease has been demonstrated again and again, and although there is no case exactly
parallel to that of the Tees valley outbreak, it is easy to understand how the cause of exceptional prevalence
of disease ovc^" a large tract of country may be overlooked ; that it has occurred before without
detection of the cause is well within the bounds of probability, and indeed the facts that have recently
come to light as to the past behaviour of enteric fever in the Tees valley suggest that the occurrences
of 1890-91 may not have been exceptional in that locality.
Whether, however, these are the first occasions on which Tees water has disseminated enteric
fever, or whether other similar outbreaks have occurred without being traced to this cause, it is clear
that tbe purely negative evidence of former years has failed to give assurance of safety.
In accepting Dr. Barry's conclusions as to the Tees valley outbreak I may again refer to the
importance which the Royal Commission has attached to the dilution to which sewage entering the
rivers is subjected by admixture with their waters, and to the comparison made in the Commission
report between the amount of pollution of the Caterham well and the amount of pollution of the rivers
Thames and Lea.
What has taken place in the Tees valley illustrates the impossibity, in our present 'state of
knowledge, of forming any useful estimate of the amount of specific matter which is required to render
virulent any given volume of water.
The Commission estimates that some half million cases of typhoid in the Thames valley would
be required to pollute the Thames to the same extent as the man in the Caterham well polluted the
water of that well, and then points out that the entire population of the valley above Hampton consists,
men, women and children, of only about one million persons.*
The Royal Commission's statement as to the Thames may be thus paraphrased for the purposes
of the Tees—
It appears from returns made by the chairman of the Caterham Water Company that the total
amount of water pumped from the well in the 14 days during which it was being continually
polluted was 1,861,000 gallons. But if the volume of water brought down by the Tees to the intakes
be taken into account, and also the fact that at least 98 per cent. of the microbes in water are removed
by filtration, it will be found on calculation that in order to produce an equal amount of pollution of the
water supplied to the Tees water consumers to that of the Caterham well, nearly 17,000 cases of typhoid
fever must occur in a fortnight in the Tees valley above the intakes, the discharges from all these cases
passing into the river as directly and in as great a proportion as did the discharges of the workman into
the Caterham well, and no part of these discharges being arrested or destroyed on their way down to
the intakes, or during the sojourn in the subsidence tanks. But the entire population of the valley
above the intakes consists—men, women and children—of only about 21,000 persons.†
That nearly 17,000 cases of enteric fever should occur in a fortnight in the drainage area of the
Tees above the intakes, the population of which is shown by Dr. Barry to number some 21,000
persons, is obviously practically impossible. Nevertheless the Tees was assuredly rendered virulent,
although by how few cases cannot be stated.
It is very much to be regretted that the circumstances in which the water supplied by Tees
companies was able to disseminate typhoid fever among the tenants of those companies was not made
the subject of complete investigation by the Royal Commission. For although there are important,
differences between the Tees and the London rivers, the fact that filtration failed to protect the
consumers of the Tees water raises questions as to the dependence which may be placed on filtration
for complete and uninterrupted protection.
* The medical officer of the Local Government Board thus concludes his prefatory comments on Dr. Barry's
report, " seldom, if ever, has the proof of the relation of the use of water so befouled to wholesale occurrence of
enteric fever been more obvious or patent."
† The case as stated by the Commission as to the Thames is in effect ae follows—one case of typhoid fever
in the case of Caterham rendered virulent 1,861,000 gallons of water distributed during 14 days.
The average daily flow of the Thames is equal to 1,350 million gallons.
Tn 14 davs the flow would be 1.350 million X 14=18.900 million grallons.
To produce pollution of this same amount of water to the same extent as at Caterham,
cases ot typhold fever would be required.
If however, 98 per cent. of micro-orsranisms were removed bv filtration then
cases would
be required, whereas the population only numbered about one million.
The case as to the Tees may thus be similarly stated.
The flow per diem of the Tees in time ot drought has been estimated at 45.000.000 gallons, therefore apply.
ing the preceding argument to the Tees
cases in a fortnight would be required to pollute the
Tees to the same extent as the Caterham well was polluted. A number which would be considerably larger were
the average daily flow of the Tees considered, as in the calculations referred to concerning the Thames.