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53
In London the responsibility for disinfesting houses is placed upon the owner
of the house, and for disinfesting articles upon the sanitary authority.
The Council's scheme for co-operation with the landlord and the technique
used for sulphur disinfestation were fully described in my Annual Report for last
year. No change look place in so far as co-operation was concerned and only minor
alterations were made in the method of disinfestation. The changes which took
place in the technique related only to the method of application of the sulphur.
When sulphur candles are used for disinfesting a room the diffusion takes place
slowly. Immediately above the candle the sulphur gas is most dense, but the density
gets less until it reaches the ceiling and it appears to fall away slantingly. It was
thought, therefore, that if half-pound candles were used and placed in different
parts of the room the saturation with the sulphur vapour would become more rapidly
uniform, and furthermore, if some of the sulphur candles were placed at table height
the gas would reach the ceiling quicker. It is not necessary to worry about its
reaching the floor because as it is heavier than air it will ultimately come to rest at
the lowest point.
The Council's scheme also provides for the periodic re-inspection by the woman
sanitary inspector of houses which have been disinfested. During the year it was
found that 75 rooms were re-infested, all of which were treated again. In the case
of the second disinfestation, however, we do not ask the owner to co-operate ; we
content ourselves with a further sulphur treatment of the room.
At the beginning of 1934 every house which had been disinfested was specially
inspected in order to ascertain in what percentage recurrence of infestation took
place.
Since the scheme started in August, 1932, 846 rooms, occupied by 444 families
in all, have been disinfested. Of these, 742 were disinfested by sulphur once, 75 on
two separate occasions because of re-infestation, and the remaining 29 by other
chemicals. Thirty-three rooms disinfested by sulphur once, were found to be reinfested,
and 17 of those disinfested twice were found to be re-infested. These
figures would seem to show that the scheme for sulphur disinfestation described in
my annual report for last year is efficacious in one treatment in approximately
85 per cent. of cases.
In October my attention was drawn to a chemical used for the treatment of
wood infested with the Death Watch Beetle—Ortho-dichlor-benzine—and it seemed
to me that it might be possible to use this chemical for "debugging." It was
accordingly tried. It is in liquid form but as it dries in a room it gives off a vapour
which affects the eyes and throat and so it is necessary for the disinfestors to use
masks. It is obnoxious to the bugs. It seems to be capable of driving them from
behind the skirting boards and architraves if the adjoining walls are sufficiently