This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Which serum is used for testing streptococcal pyrogenic toxin? 
Select and explain. 
A. Convalescent human serum, B. Serum from patient of acute scarlet fever, C. Horse serum, D. None of the above
A: Convalescent human serum
Answer: A: Convalescent human serum 
Explanation: Ans. is 'a' i.e., Convalescent human serum Tests related to pyrogenic toxin (erythrogenic /Dick toxin) of streptococcus There were two historical tests which were used : i) Dick test : Intradermal Injection of toxin in a child produces erythematous reaction if he/she is susceptible to scarlet fever. ii) Schultz scharlton reaction : It was used as a diagnostic test for Scarlet fever. Blanching of erythematous rash is produced during scarlet fever on local injection of convalescent serum (As serum from patient in convalescent phase has antibodies against this toxin)