The cannula (10) has an auxiliary air duct (26) and a tubular base body, on which a suction opening (12) and a coupling section (16) are formed at end regions that are turned away from each other. A minimum fluid stream i.e. ambient air, flows through the air duct. The air duct is formed as a lockable borehole in the base body and a groove on an outward turned surface of the base body. The air duct is spaced from the suction opening and extends over the coupling section that exhibits an insertion limit (24) formed as a circular ring shoulder, where the limit is arranged on the base body.
