Astra Pharmaceutical Products, Inc.

Bengt Eve Hansson

Edward A Tischlinger

A cartridge for a prefilled hypodermic syringe of the type sealed at its forward end with a destructible diaphragm is provided with a piston-piston rod assembly in which the piston of resilient material is molded in the form of a hollow cylinder and has an auxiliary short, cup-shaped member of reduced diameter coaxially enclosed within its forward end, and sealed in yieldable engagement with the inner walls of said hollow cylinder by a transverse, annularly-shaped elastic membrane. The piston rod has a forward portion of lateral cross-section smaller than the inner cross-sectional area of the piston and slidably receivable in the latter, and a following portion having a lateral cross-section dimension greater than the inner cross-sectional area of the piston, the junction of the two rod portions forming a forwardly directed shoulder. When the piston rod is actuated, the forward reduced portion slides forwardly in the piston until it engages the auxiliary member and causes such member to distend forwardly, while the main body of the piston remains stationary. Continued actuation of the piston rod then brings the shoulder formed by the following rod portion into engagement with the main body of the piston to cause the piston to move as a whole within the syringe cartridge.

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Holden, MA, United States of America

Bengt Eve Hansson