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(6) Again with chloramine the water retains its sterility for a much
longer period than with chlorine alone, e.g., water containing
0.5 parts per million when the baths are closed at night time
would be found to contain very little chlorine on the following
morning, whereas with chloramine the depreciation of chlorine
would be very small.
Other methods of sterilisation were investigated, and the Medical
Officer of Health is indebted to the London School of Hygiene and Tropical
Medicine for the assistance rendered by them in furnishing data of the
methods and experiments carried out in other countries, including particularly
that of ozonisation. In the result the Medical Officer of Health was
able to report that so far there was no conclusive evidence available of the
advantages of ozonisation as a sterilising agent of water in public swimming
pools. The high cost of the installation of the necessary plant may be one
reason for retarding its adoption.
The chloramine method was accordingly installed at the Marshall
Street Baths. Regular reports submitted by the bacteriologist on the
condition of the water in the Council's swimming pools go to show that the
water in the pools is maintained at a high degree of purity throughout the
year.
Mosquitoes.—In the early part of the summer several complaints were received
from residents and others in the neighbourhood of Chelsea Gardens of nuisance by
mosquitoes.
Investigation by the Sanitary Inspector having failed to reveal the breeding
ground, the City Council arranged for an expert entomologist from the London
School of Hygiene and Tropical Medicine to undertake an investigation and to
report upon any methods of prevention necessary. The entomologist reported that
his first visit to the area was on the 9th May and the inspection continued until the
29th June. Between those dates he heard many complaints of mosquito "bites"
and the effects thereof upon the complainants. Tubes for the collection of specimens
were distributed and among the insects obtained were non-biting midges (Chironomus)
and some mosquitoes, all of which were female (Culex Pipiens).
A number of the mosquitoes contained blood and some in fact were caught feeding
on humans.
Every likely source of breeding place was searched and examined including the
London County Council Pumping Station, the City Council's Stone Yard, Refuse
Disposal Depot at Grosvenor Canal, and Disinfecting Station, a barge repairers'
enclosure and the premises of a large firm of builders.
(9069) F 2