butt 40 of the blade 12 rides and against which the rear wall 54 of butt 40 is held in positively locked position when the blade 12 is fully extended to the operative position of fig8 the handle portions 11a and 11b and the liners 21 and 22 each have corresponding curvalinear recesses in their lower walls to define an opening 55 through which a person 39 s finger may extend to engage the base 28 of spring 27 in manipulating the knife to retract the blade 12 fig9 the knife is shown in fig1 and 8 with the blade 12 in its fully extended or operative position and the knife is shown in fig5 with the blade in the fully retracted or inoperative position as illustrated in fig5 the lower surface of blade 12 rests against leaf spring 31 depressing it within recess 50 and bringing it into supporting engagement with butt 40 or blade 12 so positioned leaf spring 31 urges guide pin 43 upwardly above track 36 and into positive locking relation with the vertically extending stop position 45 confining the blade 12 within the handle 11 assuming it is desired to move the blade 12 from the closed or inoperative position of fig5 a person places a thumb or finger on the serrated surface 42 on the upper edge of butt 40 of blade 12 and pushed downwardly.