sliding member 6 many other systems for latching the trigger may be envisaged without departing from the scope of the invention fig5 and 6 show an alternative embodiment of the resilient system of fig1 through 3 in which the tang 17 which may be molded at the same time as the trigger 13 from an appropriate plastics material for example is replaced by a curved leaf spring 20 fastened at one end to the trigger and having its curved free end 20a cooperating with a recess 18 analogous to that of fig1 through 3 fig7 schematically represents another embodiment of a knife in accordance with the invention in which the member controlling displacement of the blade 1 consists of a plunger 21 partially engaged in the handle 22 and movable in translation perpendicular to the longitudinal axis of the handle the plane in which the plunger 21 moves is parallel to the plane of the blade and to that in which the trigger 13 of the previous embodiments moves the plunger 21 comprises an outside part 21a and a part 21b adapted to enter the handle 22 in the form of a trapezoidal wedge of which the inclined rear flank 21c cooperates with a corresponding inclined surface 23 formed on a member 24 fixed to the inside of the handle the front inclined flank 21d of the wedge 21b cooperates with an inclined surface 25 of a blade carrier 26 analogous to the blade carrier 6 of the preceding embodiments a return spring 27 is disposed between the member.