IV. INVESTIGATION OF C. DIPHTHERIAE
83
reaction around the site of injection (Table I). If the individual is immune,
the antitoxin present in his blood and tissue fluids will neutralise the toxin
and block the reaction. A similar amount of boiled toxin (lOO°C for f h) inoculated in the other forearm should not elicit any reaction unless the
individual is sensitive to the foreign proteins in the preparation (pseudoreactions).
The non-specific skin reactions usually reach a maximum within 48-72 h
and then fade, in contrast to the specific positive reaction which becomes
more intense after 48 h and persists up to 72-96 h after inoculation in the
case of a non-immune individual.
The various types of responses are summarised in Table I.
T A B L E I
Various responses to Schick test
Schick
Schick test
control
Results,
probable
After
content of Interpretation
Type of reaction
48 h 72 h 48 h 72 h
antitoxin
of results
Redness
> 10 mm
in diameter
Lack of
reaction
Partial
reaction
Partial
combined
reaction
+ t + + - - Positive
< 0433
AU/ml
-
-
-
- Negative
>0.03
AU/ml
negative
> 0.03
AU/ml
+ - + - Pseudo+ + + + - Pseudopositive
(combined)
reaction
< 0.03
AU/ml
Non-immune
Immune
Immune
but
sensitive
to foreign
proteins
Non-immune
and
sensitive to
foreign
proteins
~~
~
+, + +, + + + = different degrees of sensitivity. The reaction is usually
erythematous and of different sizes-a function of the degree of lack of immunity.
A positive reaction is considered starting from an area of 10 mm diameter (+) up to
20 (+ +) or 30 (+ + +); sometimes the centre of the area is raised, erythematous,
and the periphery looking like a cockade.
- (negative reaction) indicating a level of about 0-03 AU/ml or more, in the
circulating blood.