Naegler's reaction is due to which toxin of Cl perfringens -

Ans. is 'a' i.e., Alpha toxin o Naegler's reaction detects alpha toxin (phospholipase or lecithinase C). When Cl. perfringens is grown on a medium with the antitoxin spread on one half of the plate, colonies on the other half without the antitoxin will be surrounded by a zone of opacity. There will be no opacity around the colonies on the half of the plate with the antitoxin, due to the specific neutralisation of the alpha-toxin.