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64
were unbalanced, only low forms of animal life (eggs, larvae and nymphae of midges,
water beetles, which had flown from dried-up ponds, and occasional batrachians) and
of vegetable life (confervoid algae) reaching the Metropolitan Water Board water,
with which these, mostly concrete lined, baths and lakes were filled. The absence
of fish, snails and higher marine plants allowed the flora and fauna dispersed throughout
the water as plankton to increase without limit.
One effect of the planktonic and microscopical nature of the flora was that in the
abstraction of carbon dioxide from the calcium bicarbonate, which forms most of the
"hardness"-producing matter in the London water, in accordance with the well
known equation of photosynthesis nCa(HC03)2 + light + chlorophyll (CH20)n
+ nCaC03, the cells of the organisms (usually protococcus) took up the carbohydrate
which th6y had formed and multiplied rapidly whilst insoluble carbonate of
lime separated, the turbidity of the water increasing, and a mud of calcium carbonate
and dead cells sank to the bottom, or, during swimming hours, was dispersed as a
greenish grey mud throughout the water. This mud formed a favourable habitat
not only for protozoa but for " red worms," the larvae of midges (chironomus),
developed from jelly-like masses of eggs laid by the insects at the water's edge.
These larvae feed on the mud at the bottom, coming to the more highly aerated upper
layers of water from time to time to breathe. The surfaces of the bathers' bodies,
and possibly other excretions than sweat, furnished sufficient nitrogen and salts
for both the organisms mentioned and a rich bacterial flora to flourish. It should,
however, be stated that there is some evidence that after a time bacteria decrease
in numbers owing either to the activity of protozoa or of bacteriophage or both these
agencies.
It was sought to remedy this state of affairs by the use of copper sulphate to
kill green growths, and of bleaching powder to sterilise the water, besides allowing
a considerable volume of water to flow through the bath or pond.
These attempts met with only partial success. Green growths seem to become
immune to copper salts, which also tend to separate from solution if the water is
alkaline, which it must be if there is much vegetation or if bleaching powder is added
to it. Bleaching powder produces a deposit, and, apart from bacterial contamination
which is kept under by this reagent, the turbidity of the water is a great source of
danger.
Consider a bath newly filled with water to which appropriate proportions of
copper sulphate and bleaching powder have been added and which is bright and clear.
Some hundreds of bathers use it daily, many of whom are not clean—having come
direct from work or school. Some may have washed their feet in a perfunctory way
in the foot baths which are usually provided, but in most cases they introduce an
appreciable amount of pollution. In my report of 1927 (p. 49) I stated that " it was
sought to ascertain the average contamination introduced by a bather by comparative
analyses before and after use of the water of a small swimming bath at a school.
Having regard to the respective weights and surfaces of the children using the bath
and of adults, it would appear that a not very clean adult would contribute while
in the bath about 0.8 gramme (say 12 grains) of nitrogen in all forms and 1.4 grammes
of chlorions. It is probable that the preliminary use of a shower bath and other
precautions would reduce this amount appreciably."
Since treatment of water in the baths was found ineffective, the Parks Committee
fitted two baths with plant for filtration and chlorination. In these the water
can be withdrawn continuously, as desired, from the bath by pumping from an outlet
at the bottom of the deep end, treated with coagulants (aluminium sulphate and an
alkali) filtered through sand, and all insoluble pollution having thus been removed,
treated with chlorine either as gas or in bleaching powder and returned by a cascade,
where it is aerated, to the shallow end of the bath.
The results obtained in these baths and in others which were subsequently
fitted with filtration plant have been extremely satisfactory. After a very short
period the attendants were able to work and control the plant satisfactorily, and the
water, even when the number of bathers has been very great, has been kept sufficiently
clear for articles lying on the bottom and sides at the deep end to be visible.
Very little trouble has been experienced with green growths, although in some cases
in high summer a slight growth on the bottom has shown that the chlorinated water