A medical injector comprising: a body having a distal end and a proximal end; a displaceable plunger disposed in said body, said plunger having a plurality of spaced-apart ratchet teeth disposed along the length thereof; at least one indexer formed to engage said plunger, wherein said indexer is configured to allow said plunger to displace distally towards said distal end of said body but not proximally towards said proximal end of said body; and, an actuator having an engagement portion formed to engage one or more of said ratchet teeth, wherein, said actuator is displaceable to a ready state, said engagement portion being displaced proximally relative to said plunger with said actuator being displaced to said ready state, said indexer preventing proximal movement of said plunger thereby allowing said engagement portion to by-pass one or more of said ratchet teeth with said actuator being displaced to said ready state, and, wherein, said actuator is displaceable from said ready state to cause actuation of the medical injector, said displacement from said ready state causing distal displacement of said engagement portion with said engagement portion engaging one or more of said ratchet teeth and causing distal displacement of said plunger with said engagement portion; characterized in that said injector further comprises: a frame-shaped rocker pivotally connected to said actuator at a first end of said rocker to rotate relative to said actuator, and pivotally connected to said body at a second end of said rocker to rotate relative to said body, said rocker having said engagement portion disposed between said first and second ends, wherein said plunger is disposed within said rocker, and said indexer and said engagement portion engage the same set of ratchet teeth. a body having a distal end and a proximal end; a displaceable plunger disposed in said body, said plunger having a plurality of spaced-apart ratchet teeth disposed along the length thereof; at least one indexer formed to engage said plunger, wherein said indexer is configured to allow said plunger to displace distally towards said distal end of said body but not proximally towards said proximal end of said body; and, an actuator having an engagement portion formed to engage one or more of said ratchet teeth, wherein, said actuator is displaceable to a ready state, said engagement portion being displaced proximally relative to said plunger with said actuator being displaced to said ready state, said indexer preventing proximal movement of said plunger thereby allowing said engagement portion to by-pass one or more of said ratchet teeth with said actuator being displaced to said ready state, and, wherein, said actuator is displaceable from said ready state to cause actuation of the medical injector, said displacement from said ready state causing distal displacement of said engagement portion with said engagement portion engaging one or more of said ratchet teeth and causing distal displacement of said plunger with said engagement portion; characterized in that said injector further comprises: a frame-shaped rocker pivotally connected to said actuator at a first end of said rocker to rotate relative to said actuator, and pivotally connected to said body at a second end of said rocker to rotate relative to said body, said rocker having said engagement portion disposed between said first and second ends, wherein said plunger is disposed within said rocker, and said indexer and said engagement portion engage the same set of ratchet teeth. a frame-shaped rocker pivotally connected to said actuator at a first end of said rocker to rotate relative to said actuator, and pivotally connected to said body at a second end of said rocker to rotate relative to said body, said rocker having said engagement portion disposed between said first and second ends, wherein said plunger is disposed within said rocker, and said indexer and said engagement portion engage the same set of ratchet teeth.