edge is preferably at an angle of between 20xc2x0 and 30xc2x0 to the cylindrical surface. The second edge is substantially perpendicular to the first edge, and at an angle of between 60xc2x0 and 70xc2x0 to the cylindrical surface.
Preferably the head of the plunger has means, such as a peg, with which an elastomeric sealing cap engages, and the locking means is also arranged on the head of the plunger, adjacent the cap. The plunger head locks into the interruption means and jams, effectively rendering the syringe useless. The plunder remains intact, filling the barrel, and acting as an anti-tamper block. If excess effort is applied in the removal it may break at the joint between the stem of the plunger rod and head. However, this is not theobject of the design as the locking feature is more than adequate to prevent reuse and the more preferable.
The locking means preferably comprises two rearward facing flukes attached to the head by a flexible connection, movable in each direction but engaging with the interruption means on withdrawal movement away from the distal end of the barrel. When engaging with for example an angled groove the head of the plunger is deflected in the barrel perpendicular to the groove so that both flukes are located in the groove, as far as the flexibility of the connection and the elasticity of the elastomeric cap will permit. Alternatively, the locking means comprises a disc attached to the head, and having a flexible periphery which slides in either direction, but engages with