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(b.) 1036 (i.e., 53.9 per cent.) were found to have
defective traps, fittings, or appliances.
(c.) 674 (i.e., 35.1 per cent.) gave no results with the
tests.
It will be noted that only 11 03 per cent. of the total infected
houses showed, with the test, defective drains, no results being
obtained from the tests in the other cases; and 53'9 per cent,
showed defective traps, fittings and appliances.
Drains and sanitary fittings are tested, as a routine, in all
infected houses, though it does not follow that, when defects are
found, such defects are the direct causes of the diseases under
investigation. They may indirectly be so.
The test used as a routine is the chemical or smoke test, and,
when a result is obtained, the drain (tested) is tabulated as
defective, but, when no result is obtained, it would be unsa'e to
state that, therefore, the drain (tested) was sound. A negative
result proves nothing with the chemical (or smoke) test. The
hydraulic (water) and pneumatic (air) tests are the only reliable
tests, but too severe for the routine testing of drains of old
buildings. The pneumatic (air) test is comparatively new, and
most delicate, but is not much used in London at the present
day. All new drains when laid are tested with water (hydraulic
test), both in sections and as a whole.
Bearing this explanation in mind, the statistics are still useful
as showing that, year by year, the number of defects found
decreases. Taking the statistics for the Parish of Lambeth
during 10 years (1891-1900), and those for the Borough of
Lambeth during 6 years (901.7), it will be noticed that the percentage
of houses showing defective drains has decreased from
22.3 in 1891 to 11.03 in 1907. Table L gives full particulars,
with the averages for the 10 years worked out, for the old Parish