Abstract: This invention relates to reciprocable sheaths for hypodermic syringes that have latches to hold the sheaths over the needle of the syringes. A spring is employed to normally move the sheath over the needle and the expansion of the spring is limited to 90.degree. of the free expansion dimension to positively move the sheaths and latches to the fully protected position. Volume numbers and graduations are placed on the exterior of the syringe plumger for greater clarity of reading.

Abstract: This specification discloses a lock for a latch on a hypodermic syringe which has a reciprocating sheath that is normally latched to cover the needle to protect persons handling the syringe. The latch is operated to withdraw the sheath to expose the needle for use. The latch shell 22 is moved longitudinally to actuate latch fingers 26. After use it is desirable to lock the latch to prevent reuse of the syringe. A user manually rotates the latch shell 20 to lock the latch in the position where the sheath is over the needle. Rotary motion causes the lugs 26 to ride up the ramps 28 and then drop into the recesses 29. Thereafter, there can be no rotation and no reciprocation of the latch. The lugs prevent rotary motion as well as reciprocating motion of the latch shell 22.