This spring lancet is armed by pulling the handle on the left side of the unit. The release mechanism is the lever bar on the side. No makers mark is present. A similar item is present in Davis and Appel's book on instruments from the National Museum of History and Technology (pg 96 figure 104), and in Bennion's Antique medical instruments reference (pg 221). The item in Bennion's is made by Savigny and is speculated to be c.1825.
The release mechanism on this item is on the side, slightly different from the Savigny piece in Bennion.