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Houses other than those in Council ownership are found to be infested on houseto-house
inspection, on inspection following investigation of a complaint, or on
enquiry into the occurrence of infectious disease, and occasionally an occupier asks
for help in eradicating the bed-bug. The number of such houses found to be infested
during the year was 361. The number in which the scheme of co-operation described
in my Annual Report for 1932, between the Council and the landlord, was put into
operation was 159, while a further 121 in clearance areas were dealt with prior to
demolition. One further house is known to have been disinfested by the occupier
after advice from the department.
2. The methods employed for freeing houses from bed-bugs. Different methods
were used by the Department during the year, in different circumstances.
(a) Sulphur dioxide, plus cleansing, as described in my Annual Reports for
1932 and 1933, was used in 119 houses, all of which, with the exception of 9, were in
private ownership. In 106 instances this method of treatment was successful on
one application.
(b) Cyanide (Zyklon B) was used for the disinfestation of 19 occupied houses in
13 blocks. In each case the occupiers of the infested dwellings were accommodated
for two nights in a block of empty houses on the Council's estate, reserved for this
purpose. The occupiers of the non-infested houses in the blocks were offered accommodation
for one night, but allowed to return to their own dwellings the same
evening if they so desired, as soon as the premises had been certified as safe. In
one instance re-infestation occurred during the year. Infestation was found to be
due to the sub-letting of some rooms in the house without the consent of the Council,
bug infested furniture being taken in in this way.
(c) In cases of light infestation, or where for any reason it was not practicable
to seal off a room, other fumigants or contact sprays were used on 48 occasions, with
11 primary failures.
(d) Washed heavy naphtha was used on 56 occasions. In 9 instances the
primary treatment was not successful, three of these being furnished houses.
In my report for last year I referred to experimental work with this substance
and to the necessity of working out a technique. It is satisfactory to report that
by the end of 1937 a satisfactory technique for the use of washed heavy naphtha in
unfurnished houses had been developed.
We started using washed heavy naphtha, or rather pseudo-cumene—that part of
naphtha which comes off at the lower temperatures—in June, 1936, and we got
satisfactory results until October, when we began to get failures. It was then found,
after some laboratory experiments in London, that the minimum lethal concentration
of naphtha for the bed-bug was .15 percent., for a period of 18 hours, and that a
temperature of 50 degrees F. was necessary for that period if this concentration was