Nagler’s reaction is a test for **alpha-toxin** production, which is specific to *Clostridium perfringens* type C. This toxin causes gas gangrene and is detected by the formation of a yellow precipitate when a reagent containing sodium hydroxide and sodium chloride is added to the culture. Other clostridial species do not produce this toxin or show a positive reaction. *C. tetani* causes tetanus, *C. botulinum* produces botulinum toxin, and *C. septicum* is associated with septicemia but not Nagler’s reaction.

**✓ Correct: C. Clostridium perfringens**