Automatic injector comprising: - a housing assembly having a central longitudinal axis; - an interior chamber located within the housing assembly, the interior chamber having an inner side surface extending in the direction of the longitudinal axis; and - a seal structure positioned in the interior chamber to form a dry compartment and a wet compartment, the dry compartment suitable for containing a dry substance and the wet compartment suitable for containing a liquid, the seal structure positioned between the dry compartment and the wet compartment, the seal structure comprising: ∘ a first end adjacent the wet compartment; ∘ a second end adjacent the dry compartment; ∘ an outer seal that sealingly engages the inner side surface of the interior chamber to prevent passage of liquid between the outer seal and the inner surface of the chamber; ∘ a rigid member in communication with the outer seal and having at least one by-pass channel; and ∘ an inner seal plug in communication with the rigid member, movable between a first position wherein the seal structure is in a sealed state and a second position wherein a flow path is created via the by-pass channel, whereby the seal structure is in a flow-through state, characterized in that the seal structure further comprises ∘ a fluid-directing member located on the second end of the seal structure, the fluid-directing member comprising a channel that is helical about the central longitudinal axis and has a fluid exit port into the dry compartment, the fluid exit port having an opening that fully faces and is parallel to the inner side surface of the chamber, such that the liquid entering the dry compartment has flow components in axial, circumferential and radial directions. - a housing assembly having a central longitudinal axis; - an interior chamber located within the housing assembly, the interior chamber having an inner side surface extending in the direction of the longitudinal axis; and - a seal structure positioned in the interior chamber to form a dry compartment and a wet compartment, the dry compartment suitable for containing a dry substance and the wet compartment suitable for containing a liquid, the seal structure positioned between the dry compartment and the wet compartment, the seal structure comprising: ∘ a first end adjacent the wet compartment; ∘ a second end adjacent the dry compartment; ∘ an outer seal that sealingly engages the inner side surface of the interior chamber to prevent passage of liquid between the outer seal and the inner surface of the chamber; ∘ a rigid member in communication with the outer seal and having at least one by-pass channel; and ∘ an inner seal plug in communication with the rigid member, movable between a first position wherein the seal structure is in a sealed state and a second position wherein a flow path is created via the by-pass channel, whereby the seal structure is in a flow-through state, ∘ a first end adjacent the wet compartment; ∘ a second end adjacent the dry compartment; ∘ an outer seal that sealingly engages the inner side surface of the interior chamber to prevent passage of liquid between the outer seal and the inner surface of the chamber; ∘ a rigid member in communication with the outer seal and having at least one by-pass channel; and ∘ an inner seal plug in communication with the rigid member, movable between a first position wherein the seal structure is in a sealed state and a second position wherein a flow path is created via the by-pass channel, whereby the seal structure is in a flow-through state, ∘ a fluid-directing member located on the second end of the seal structure, the fluid-directing member comprising a channel that is helical about the central longitudinal axis and has a fluid exit port into the dry compartment, the fluid exit port having an opening that fully faces and is parallel to the inner side surface of the chamber, such that the liquid entering the dry compartment has flow components in axial, circumferential and radial directions.