the injection mechanism (3) a piston (2) and an injection mechanism (3) with a needle (31) a spring (32) and a membrane (33). The piston (2) has a serrated crown in the lower part (21) thereof where a chamber seal exists (22) and breaks only with the interior point of the needle (31) having the ends of the piston (2) of an inferior disk (24) and a superior disk (25) that steadies the piston (2) inside the cylinder (1). Around the cylinder (1) there is a protective funnel (13) against accidental injections. The piston comprises a cap (26) which guarantees the hermeticity of the empty chamber.
