An automatic mixing device, an actuating device removably mounted to the automatic mixing device and a retractable syringe having the automatic mixing device are provided. The actuating device has an initially compressed spring and a trigger member that initiates spring decompression to drive depression of a mixing plunger of the automatic mixing device. A seal located in the outer chamber is capable of axial movement upon depression of the mixing plunger, from a first position in sealing engagement with one or more apertures in an inner barrel to a second position intermediate the apertures and vents in an outer barrel. This allows depression of the mixing plunger to force a first substance from the outer chamber through the apertures to mix with a second substance in an inner chamber of the inner barrel. The mixed substance in the inner barrel is then delivered by the syringe with subsequent needle retraction.