<prompt> Opacity around colonies of clostridium perfringens is due toTheta toxinLecithinaseDesmolaseCytokinin  <response>: Alpha toxin is produced by all thoracic clostridium perfringes. Alpha toxin is lecithinase C. Demonstrated by Naglers reaction. Nagler reaction; When Clostridium perfringes are grown in media containing 6 agar, Fildes peptic digest of sheep blood and 20 human serum, with antitoxin spread on one half of plate, colonies in the other half without antitoxin will be surrounded by a zone of opacity. No opacity around the colonies on the half of plate with antitoxin. This is due to the specific neutralization of the alpha-toxin or lecithinase C. Reference: Textbook of Microbiology; Anathanarayan and panikers; 10th edition; Page no: 259 