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With the object of securing pure cultures of B. diphtheriæ for the application
of virulence tests, attempts at isolation of the bacilli by plate culture were made
involving 475 cultivations from 324 cases, including 189 examinations which had been
originally reported as suspicious and from which diphtheria bacilli were isolated
in 17 cases. B. diphtheriæ was successfully isolated in a total of 219 cultivation
tests from 141 cases and to these, thanks to the courtesy of Dr. R. A. O'Brien and
his colleagues of the Wellcome Research Laboratories, animal virulence tests were
applied with the following results:—
Virulent 138 tests of 102 cases = 72 per cent.
Avirulent 81 tests of 39 cases = 28 per cent.
Included in the above figures were 6 cases in which original cultures were virulent
in 8 examinations and avirulent in 13 subsequent cultures.

The value of virulence tests may briefly be summed up by saying that all the
children found avirulent are at once re-admitted to school, thereby saving considerable
loss of school attendance. During the past two years it has been calculated in the
case of 33 avirulent carriers that their re-admission to school on the results of the
virulence test might in times past have involved the loss of no less than 166
months, or close on 14 years of school life, an average of 5 months for each child
concerned; for it was found in subsequent swabbings that the carrier condition
persisted after re-admission for periods ranging from one to 20 months, or even as
long as 3 to 4 years, as shown by the recent re-examination of 14 past avirulent
carriers, in 7 of whom avirulent bacilli were still present.
In actual practice the periods of absence of carriers from school varies widely
according to circumstances, but it may be stated that during the 6 months ended
February, 1923, the average duration of exclusion from school was 10.5 weeks for
virulent and 2.9 weeks for avirulent carriers. The latter period could no doubt
be reduced still further under favourable conditions.
A review by Dr. J. G. Forbes of the Schick test for diphtheria susceptibility and the
advocated prevention of the disease by artificial immunisation.
The test, introduced by Professor Schick, of Vienna, in 1913, is made by the
injection of a minute measured quantity of diphtheria toxin into, not under, the
skin. If the person injected has no natural anti-toxin in his blood or an insufficient
amount for his protection, a positive reaction follows in the form of a circumscribed
area of redness and infiltration in 24 to 48 hours at the seat of injection, thus giving
evidence of non-immunity or an absence of anti-toxin to counteract the very small
amount of toxin injected. Since the introduction of this well-known test, information,
chiefly from America, has been steadily accumulating both as to its use, and as to
the practice of active immunisation (of those found to be naturally unprotected)
by means of injection with diphtheria toxin-antitoxin mixture.
In children of both the pre-school and school age the results of the Schick test
in the percentage proportions of those giving positive reactions (i.e., the nonimmune)
have shown an age distribution closely in accordance with that of the incidence
of the disease itself and of the case mortality rate.
This agreement between the tested non-immunity, the diphtheria incidence and
mortality rate, as Park and Hughes in America and workers in this country have
emphasised, can be traced through the successive years of early life and the later
school age period. During the first 6 months the comparatively slight susceptibility