A cannula (1) comprising a central axis (2), a front end (3) and a through channel(5) coaxial or parallel to said central axis (2) and defining a peripheral wall(12) of said cannula (1), wherein A) said cannula (1) further comprises at leasttwo perforations (8) penetrating said peripheral wall (12) transversely tosaid central axis (2) B) said through channel (5) is open at said front end (3)and C) the cross section of said through channel (5) has a contraction (6) witha diameter d
