An injection device which includes a housing (12), a needle hub (38) slidable within the housing (12), a needle (40) having a distal end piercing tip (42) and a proximal end piercing tip (44), the needle hub (40) being moveable from a first position wherein the distal piercing tip (42) is within the housing to a second position wherein the distal end piercing tip (42) extends outwardly of housing (12), a first spring (23) biasing the needle hub (38) towards the first position, and a cartridge receiving member (48) mounted within the housing, and a plunger rod assembly (166), the plunger rod assembly (166) having a distal interior chamber (102) and a proximal interior chamber (103), the distal interior chamber (102) being designed to receive a cartridge (85) containing a liquid (89), the cartridge having a septum (87) and a plunger (88) to prevent exit of the liquid, and a second needle hub (91) located in the proximal chamber, a second hollow needle (92) mounted in the second needle hub, the second hollow needle having a distal piercing tip (94) and a proximal piercing tip (93), the second hollow needle being moveable from a first non piercing position to a second position whereby said distal piercing tip (94) will pierce the septum (87).
