The variable dose is dispensed by a plunger-and-barrel or bellows mechanism automatically actuated hydraulically, pneumatically or by solenoid - alternatively a rotary pump or an electronically-controlled restricted passage can be used. This is mounted near a reservoir containing more than the unit dose, and is fixed to a flexible wall through which the power pulses are transmitted. Means are included to prevent germ colonisation of the reservoir, typically in the form of a vessel subjected to the effect of sterilising material, and resealing of the outlet can likewise be effected hydraulically, pneumatically or electrically, or heat can be applied. A permanently mounted or detachable syringe nozzle can be included.
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