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31
Report of the County Medical Officer—General.

Typhoid
fever
death-rates
and caserates,
London.
The death-rate in each year since 1868 in relation to the mean death-rate of the period 1869-1913
is shown in diagram (P).
The notified cases in each week of 1913 may be compared with the average weekly notifications
of the period 1890-1913 on reference to diagram (Q).
The monthly case-rate and case-mortality in each of the years 1891-1913 in relation to the
mean of the whole period is shown in diagram (R).
Last year reference was made to the comprehensive report, which appeared in 1912, giving an
account of the experience gained in the campaign against typhoid fever instituted by Robert Koch
in South-West Germany in 1904. The point of view therein illustrated and defended in great detail
was one which had been elaborated as the result of the eight years' subsequent examination by
German bacteriologists of Koch's hypothesis. Koch held that typhoid fever was due to an organism,
the natural habitat of which is the human body, and he and his followers were led to assume that
typhoid fever can be stamped out by the institution of sufficiently stringent measures directed against
the typhoid bacillus whenever and wherever it is found directly associated with the healthy or diseased
human body. Some of the difficulties arising out of these assumptions were considered in last year's
report.
During 1913 an important report appeared which throws some very interesting side lights upon
Koch's hypothesis and upon the general question of the aetiology of typhoid fever. In his 10th Report
on Research Work, Dr. A. C. Houston. Director of Water Examinations, Metropolitan Water Board,
attacks once more, and in greater detail than he has done hitherto, a problem which has been for some
years engaging his special attention. Dr. Houston has made many attempts to isolate the typhoid
bacillus from raw Thames water. Save in two instances he has been unsuccessful, but he has realised
from the first the limitations of the method of examination which has been employed. The bacteriologist
is faced with the task of endeavouring to pick out the typhoid bacillus from among vast numbers of
other organisms, of endeavouring in fact to discover the needle in the bundle of hay ; or, rather, it might
be said of predicting how many needles may be expectcd to be present in an almost unlimited number
of haystacks. Thus, as the outcome of much labour he is only able ultimately to assert, under the
strict conditions of limitation necessarily observed, that in the small number of bundles of hay examined
with the particular object in view, he has only twice found what appeared to be a needle. Dr. Houston
has employed two somewhat diverse methods of arriving at his results and the general conclusions are
given oa page 11 of his report. It transpires that neglecting the two apparently positive results, it
may be inferred that the typhoid bacillus will not be found in 9 c.c. of raw river water, judging by one
of the methods employed, or in 17 c.c. of raw river water, judging by the other method. The quality
in this particular connection of filtered water is assumed to be 1,000 times more satisfactory than that
of raw water, and hence absence of the typhoid bacillus may be generally inferred from samples of
9,000 c.c. or 17,000 c.c. of filtered water, i.e., from 10 to 20 litres, or say, 15 to 30 pints of such water.
Dr. Houston (pp. 6 and 7 of his Research Report) discusses two problems : " Whether typhoid
bacilli reach the consumer singly or in clumps, and whether one or a number are necessary to start the
infective process," problems which, he says, " are of extreme interest to epidemiologists. '
He states that, assuming a customary draught of water to be half a pint, we have to " face the
circumstance that although the typhoid bacillus may not be present in 9047 c.c, it may yet be present
in ,say, 9152 c.c., so that on the average we may ingest it once out of every 32 draughts.'' He adds,
" If a single typhoid bacillus ingested with a draught of water can conceivably infect with typhoid fever
a susceptible individual, this would be a serious matter, but if, as seems more probable, a number are
always or usually required to start the infective process and they are present as ' individuals ' and not
as ' clumps ' and are equally distributed throughout the filtered water, infection might seldom, if
ever, take place."
(a) The Infectious Disease (Notification) Act, came into force in 1889. (b) See footnote (c), page 6.