Blood-gas syringe

Claim 1

A syringe, which comprises; a cylindrical barrel having a first open end for receiving a plunger and a second open end adapted to mount a needle on the opening thereof; and a plunger slidably mounted in said barrel, said plunger being withdrawable from said barrel through said first open end and said plunger comprising; a. means for receiving a force to move said plunger in or out of said barrel, b. an elastomeric piston adapted to form a sliding seal with the inner walls of said barrel, said piston having an upper end and a lower end and a bore therethrough communicating between said upper and lower ends, c. a shank joining said means (a) to said piston (b); d. an extension of said shank passing through said bore and extending beyond the lower end of said piston, said extension preventing the piston from contacting said barrel second end; e. a chamber defined by said second open end of said barrel and the lower end of said piston when said extension is in contact with said second open end; f. an inert fluid disposed in said barrel between the second open end thereof and said piston, in a volume in excess of that required to fill said chamber and the bore of said needle; said extension having means thereon to permit the entire surface of said piston lower end being in open communication with the outside of said barrel through said second open end when said extension is in contact with said second open end.