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evacuations of cases sufficiently severe to lead to the patient remaining in bed daring a much longer
period than two days; and had the company pumped five times as much water, this might have been
found to be infective. If so, the occurrence of 100 cases of typhoid fever of average severity in a town
above the intakes, a very possible event at any moment, might be thought of, instead of the half-amillion
cases mentioned in the report of the Commission.
I follow the Commission in leaving out of consideration (for the purposes of this particular part
of the discussion) all questions of the opportunities for the destruction of the typhoid bacillus in the river.
I do not of course propose to assume that the pollution of a well is parallel to the pollution of a
running stream, but inasmuch as I understand the Commission to suggest that we should draw
deductions as to the safety of Londoners from the comparisons it has itself made between the amount of
water polluted in the Caterham well and the London rivers, I think it well that this point should be
discussed.
Viability of typhoid bacillus,
The Commission in referring to the length of time the typhoid bacillus retains its vitality after
leaving the human body, says, " it appears to be the belief of bacteriologists that such dejecta begin
to lose their virulence after a very few days, and the longest period for which the typhoid bacillus has
as yet been found to retain its vitality when in fecal matter, does not exceed 15 days."
Even the shorter period would, however, in point of time, give ample opportunity for typhoid
dejecta in the sewage of several of the larger towns on the banks of the Thames to reach the intakes of
the water companies while still virulent.
It is very difficult to determine by experiment to what extent typhoid bacilli can be carried from
such sources as low down the river as the intakes of the water companies.
The most important experiments which were made with a view to obtaining information on this
subject, were conducted by Professor Hay Lankester, and are thus referred to in the report of the Royal
Commission. " It is certainly true that no pathogenic bacteria have yet been detected in the water of
these rivers; but to this it is answered with much force, that the samples used in the ordinary method
of examination by plate culture are so excessively minute that it cannot be inferred, from such want
of detection in the sample, that the bacteria are really absent from the bulk. This objection is,
however, met, at any rate to a considerable extent, by the experiments carried out by Professor Ray
Lankester. In some of these a considerable volume of raw river water was passed through a
Pasteur-Chamberland filter, which, while it allows the water to percolate, holds back all the bacteria ;
while in others the substance for examination was obtained by taking some of the gelatinous layer of
living microbes that had accumulated on the surface of a filter of one of the London water companies.
The material obtained by these several processes from a relatively large bulk of water was then subjected
to the most delicate of modern tests for the detection of typhoid bacilli, namely, that known as the
method of Parietti, and in no case was this bacillus found to be present. Experiments such as these,
though they cannot be said to demonstrate the total absence of pathogenic bacteria from the river water
before it enters the filter beds, yet add largely to the probability of their being present, if at all, only in
very small numbers."
I do not gather that Professor Lankester is, without further experience, disposed to regard the
testing of the deposit on the filter beds as altogether reliable, for although in his statement he says,
" We have the bacteria and solid particles filtered off at Ditton from many millions of gallons of water,
and in this concentrated material Parietti's method would surely reveal the typhoid bacillus if present."
he later adds, " No doubt it would be interesting and important to make continuous examination for it
in this deposit once a week during a series of years." And again still later in giving evidence when
asked, " Would it be fair to represent that material for bacteriological purposes as the concentrated,
say, essence of the raw material, the worst essence that you could get of the raw material ? " he replied,
" I should say so, with this qualification of course, that some destructive changes may have already
been set up in the deposit, and on that account I obtained the deposit at as early a period as possible ;
that is to say, from a comparatively newly started filter bed." The matter collected on the Chamberland
filter, Professor Lankester thinks free from this objection.
It must not, of course, be assumed that the quantity of concentrated " material" from the filter
bed, which must have been actually examined by Professor Lankester, contained the organisms of the
many million gallons of water which passed through the whole of the filter bed : the amount of material
examined must be thought of as being related to a quantity of water, a fraction of the total amount
filtered, having the same proportion to this total amount that the area occupied by the concentrated
material examined by Professor Lankester bore to the total area of the filter bed.
These experiments of Professor Lankester do not do more than show that the typhoid bacillus was
not present in certain quantities of Thames water, of which we do not learn the exact amount, and I do
not myself attach any great importance to them. Considering the varying conditions of a river and the
varying amount of of typhoid fever present in towns above the intakes, it is quite possible that the
typhoid bacillus might be present at one time and not at another. Indeed, Professor Lankester (apparently
employing a different method) himself failed to find the bacillus in the sewage of Oxford. It is
true that his investigation was made at a time when typhoid fever was not known to exist in the town,
but the excreta of typhoid patients must often at other times have gained access to the sewer, and even
during the time of his investigation unrecognised cases of typhoid are not unlikely to have been present
in a population of the size of that of Oxford. His tests of Thames water moreover were made at a
period of the year when the number of cases of this disease is in England usually below the average.
Number of organisms required to produce disease.
I need not refer to the evidence as to the necessity for a certain number of pathogenic organisms
being required to produce disease, for the reason that there is no knowledge of how few of the typhoid