The invention relates to a medical instrument for an endoscope, the instrument comprising a flexible outer insertion tube (5) having a tubular wall possessing a proximal portion (6) for connection to an actuator support (3) and a distal portion (7) presenting an outlet section (8) and connected to a folding mechanism. The instrument comprises:an outer insertion tube (5) includes closure systems (10, 11) for closing its proximal portion (6) and its distal portion (7) to define an internal chamber (13) communicating beside the distal portion with the outside of the tube via at least one orifice (15) formed through the distal portion of the tubular wall, and beside the proximal portion, with a substance transit source (19) anda series of flexible tubular ducts (21i) mounted independently of one another inside the insertion tube (5) passing through the chamber (13) and the closure systems (10, 11) in order to open out to the outside of the outlet section (8) of the distal portion (7) of the tube.
