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8
last three years been once again able to emigrate. Furthermore, the reduction in London during the last
10 or 12 years of the number of men of the homeless class has probably had some slight influence also on
the trend of male deaths at ages 40 and upwards.
Measles.
The deaths from measles in London during 1921, numbered 244, as compared with 1,016 in 1920.
The mortality was .05 per 1,000 living, the lowest rate recorded in London. The monthly deaths from
measles in London since 1890, are shown in the diagram on page 44 in Part II. of this Report.
Scarlet fever.
There were 32,738 cases of scarlet fever in London in 1921 (52 weeks) as compared with 22,705
in the preceding year. The deaths numbered 292, giving a death-rate of .065, the corresponding figure
for 1920, being .045. The monthly incidence of scarlet fever cases in London since 1890, is shown in the
diagram just referred to, and in connection with it the prevalence of 1921 is discussed. During the
first quarter of this year there have been 5,486 cases; this is very much in excess of the average for
the quarter and has indeed only been exceeded twice since 1890, i.e., in 1908 and last year.
Diphtheria.
The number of cases of diphtheria notified in 1921 (52 weeks) was 16,319, as compared with
13,780 in 1920. The deaths in the calendar year were 1,150, the corresponding figure for 1920, being 1,023.
The number of cases of diphtheria in London in the year 1921, exceeded that in any year since 1890,
when notification of the disease became compulsory. The annual returns of the Ministry of Health on
the incidence of notifiable infectious disease show that the excess in incidence of notified diphtheria in
London over administrative counties in the rest of England and Wales has increased since 1911, the year
when the returns were first prepared. In the first quarter of this year the cases notified numbered
4,177 which exceeds the corresponding figure for last year by 34 cases and is the highest ever notified
in any first quarter.
Seasonal
incidence
The seasonal incidence of the principal infectious diseases in the period 1911-1920 is shown in
the diagram on page 9. It is interesting to make comparison between these contours and those for
the preceding decennium, shown in the report for 1910, page 50. The number of cases of smallpox
was too small to give a seasonal contour.
Report by
Dr. J.
Graham
Forbes on
virulent and
avirulent
Loeffler
bacilli
(K.L.B.)
At the end of March, 1921, application was made to the school medical officer by Dr. R. A.
O'Brien, Director of the Wellcome Research Laboratories, Brockwell Hall, for the supply of strains of
diphtheria bacilli obtained in culture from the throat or nose of school children not suffering from clinical
diphtheria, for the purpose of testing such strains for virulence and comparing them with strains from
cases of the genuine disease. Dr. O'Brien's request was very readily complied with as providing a much
needed opportunity of dividing the school children, who were found to yield morphological diphtheria
bacilli in culture, into groups of virulent and avirulent carriers. By means of the virulence test it has
been possible to allow the immediate readmission of all those found carrying the avirulent organism,
without the delay of repeated bacteriological examination. The return of children, though carrying
organisms morphologically and culturally indistinguishable from the diphtheria bacillus, but avirulent,
has led to no harmful results. There is, moreover, no evidence yet forthcoming that the avirulent strain
of diphtheria organism can become virulent. It is, however, recognised that in exceptional instances
virulent and avirulent strains may exist at one and the same time and be obtained in the same culture
from the throat or nose. This exceptional occurrence has been found in two cases (L.S. and W.P.)
out of a total of 246 children, or less than 1 per cent., whose diphtheria cultures were sent to the Wellcome
Research Laboratory for the virulence test during the past year. The two strains may also uncommonly
alternate. The rare co-existence or alternation of the two types is regarded as being due
to reinfection with one or the other strain of organism. The risk of the carriers of the avirulent
organism becoming infected with virulent K.L.B. is of course no greater than that of an ordinary
person becoming infected with virulent diphtheria germs. "Though indistinguishable morphologically
and culturally," says Dr. Eagleton, "efforts at the Wellcome Research Laboratory have
quite failed to change the virulent into the avirulent and vice versa in the test tube." Further, no
success has attended the attempt to produce immunity to virulent strains by the injection of massive
doses of the avirulent strain. Guthrie and his associates, publishing the results of their observations
on diphtheria carriers in the Johns Hopkins Hospital Bulletin, November 1920, find no proof that
avirulent bacilli can acquire virulence or give rise to clinical diphtheria, hence avirulent carriers are
not a menace to anyone ; but the carrier of virulent K.L.B. occupies quite a different position.
Needless to say the rare combination of virulent and avirulent strains is a complication difficult
otherwise to explain or guard against save by the aid of periodical re-examination. Five cases or 2 per
cent. of the total 246 tested, which were originally proved to be virulent by 9 separate examinations,
yielded avirulent strains in 11 subsequent re-examinations and were in consequence re-admitted to
school without harmful results.
The children whose cultures prove virulent are excluded until re-examination on three successive
occasions proves negative or until (as in the five cases quoted) the diphtheria bacillus isolated proves
to be avirulent.
For the 12 months between April, 1921, and March, 1922, a total number of 6,973 bacteriological
examinations in stained film preparations from cultures from the throat and nose were made, of this
total 5,795 were passed as negative. In 697 or 10 per cent. K.L.B. were found and in 481 or 7 per
cent. suspicious organisms resembling K.L.B. were reported, or in a total of 1,178 K.L.B. were found or
suspected.
With the object of isolating the diphtheria bacillus in pure culture, where possible, for transmission
to the Wellcome Research Laboratory for virulence tests, detailed investigations by plate culture
and sub-culture were carried out in 568 cases represented by a total of 802 separate examinations, and
selected from the 1,178 in which K.L.B. or suspicious organisms were found in the preliminary cultures
from the throat or nose.
The diphtheria bacillus was successfully isolated in 334 examinations of 246 cases, including 74
which had originally been reported as suspicious. In 171 where the organism was found in preliminary
cultures attempts at isolating in pure culture failed, the plate cultures yielding diphtheroid organisms