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somewhat belated, as probably ninety per cent. of the houses have
already an intercepting trap of some form or other in the house drain'
and in regard to the future it is doubtful whether any authority would
go further than to make the use of the trap optional, in which case I
think that the majority of residents would prefer that their drains were
aerially disconnected with the sewer.
Until the rodent is extinct the intercepting trap will be able to
claim one distinct advantage, viz.—that it keeps rats out of the house,
for it seems to be established that unless driven by fear, a rat will not
dive through water unless it can see day light on the other side.
Without exception the appearance of rats in a dwelling house is
regarded with horror, and, further, the part played by the rat in the
transmission of disease is such as to justify every possible means of
excluding it from the house.
During 1912 all complaints of rats which have been received in
Hampstead have been traced to untrapped sewer connections, and
whenever such a complaint is received the line of enquiry adopted is
always in that direction.
The great objection to the intercepting trap is without doubt its
liability to become choked, but the risk of trouble in that direction can
be obviated by the adoption of some form of stopper for the raking arm,
which cannot be shaken out by the vibration of passing traffic, by special
attention being adopted to ascertain that no cement or obstruction of a
like character is left behind in the trap by the builder who lays the
drain, and a careful enquiry into the possible existence of a running
syphon trap in the drain outlet under the road before an intercepting
trap is fixed within the curtilage of the premises. Any double trapping
of that kind without the ventilation of the intervening drain is bound to
result in obstruction and difficulty in working.
Another noteworthy conclusion of the Departmental Committee is
that the fresh air inlet is of small importance in a drainage system, and
that it might be omitted without disadvantage.
The conclusions arrived at in regard to the ventilation of sewers,
and the injurious effect of drain and sewer air, are especially interesting
in view of the investigation carried out in Hampstead in 1905, the