(1) A toxic filtrate obtained from the haemolytic
streptococcus associated with an acute case of
scarlet fever was used intradermally in a
dilution of l' in 1000 and in 0.2 cc. amounts as
the skin test dose for the purpose of the Dick
test. The reaction depended on the quantity of
toxin injected and on the particular toxin,
deemed specific, employed. The standardisation
of a selected toxin is a difficult matter and can
only be estimated after a large number of tests
have been made in relation to susceptibility and
non-susceptibility to scarlet fever.
(2) The toxin adopted and used in testing 1879 persons
not suffering from scarlet fever indicated
a susceptibility rate just ahead in time of the
known age-incidence of the disease. It yielded
a high percentage positive rate in the early
years of life, the highest incidence, 85 per cent,
falling on the 4 to 5 age period. This shows
that if the production of active immunity to
scarlet fever is adopted as a general preventive
measure, in the same way as has been in the case
of diphtheria, it, should be carried out in the
under-school-age period. The average susceptibility rate for all age periods was
47.8 per cent.
(3) The Dick test determined susceptibility or
immunity to scarlet fever. Twenty-seven persons
who previously gave positive reactions to the
test and were presumably susceptible to scarlet
fever contracted the disease whilst not one of
fifty-eight persons who were negative to the test
took scarlet fever on direct exposure.
(4) In the large majority, 85.4 per cent, of 269
individuals suffering from scarlet fever the
Dick test was positive in the first four days
of the disease and became negative as convalescence
advanced. Only 8.4 per cent gave positive
reactions from the beginning of the third to the
end of the fifth week. It is frankly admitted
that negative reactions have occurred in acute
cases and positive reactions in late convalescent
cases, and while certain suggestions may be made
to account for these, an adequate explanation of;
such apparent anomalies is not yet forthcoming.
(5) On the whole the results obtained with the Dick
test bore a definite relationship to immunity
to scarlet fever. They agreed with those obtained
by various investigators and were in
support of the claim that the Dick test is a
valid/
8 0 .
valid one and pari passu that the haemclytic
"Streptococcus scarlatinas" is most probably the
etiological agent of scarlet fever.
(6) The Dick test affords valuable corroborative
evidence on which to base a diagnosis of scarlet
fever and may even be regarded as the deciding
factor in those cases where the clinical evidence
is of a doubtful or conflicting nature. The
test was also turned to account in the administrative
supervision of the clinical side of the
hospital. The practical applications which the
test may furnish as a diagnostic weapon and at
the same time as a useful measure in hospital
administration may be summarised as follows:
(a) A negative Dick test in the first four
days of a disease, or a strongly positive Dick
test after the fourth day, and more especially
after the fourteenth day of a disease, were
testimony that the disease was not scarlet fever
unless clinical evidence was to the contrary.
(b) A negative reading of the test, however,
in the first four days of a disease simulating
scarlet fever meant that the diagnosis of
scarlatina would have to be withheld until
verified later by clinical signs alone.
(c) The possibility of an early interpretation
of the reaction was of great clinical value.
This was specially useful in providing a ready
means of preventing exposure of positive Dick
reactors to scarlet fever by too hasty an admission
to scarlet fever wards. Once exposed to
scarlet fever positive reactors could be isolated
or could receive prophylactic doses of scarlet
fever antitoxin within a day of the application
of the test.
(d) Negative Dick reactors could be placed
or allowed to remain in scarlet fever pavilions
without much fear of their taking scarlatina.
(e) Oases in whom the diagnosis was in
doubt and who by reason of single or repeated
Dick tests were considered non-scarlatinal need
not be kept in hospital for the usual four to
five weeks’ supervision. Dick negative reactors
who came into actual contact with scarlet fever
could be sent home with equanimity.
(f) The test enables one to discriminate
in the selection of a nursing staff for scarlet
fever pavilions and to ensure that only nonsusoeptibles
shall be so employed. Susceptible
nurses could be prepared for scarlet fever duty
by a process of active immunisation which is now
available and which is actually in routine use
in some fever hospitals
