A two-chambered syringe comprising: a. an outer barrel with an open end; b. an inner barrel movable in and out of said outer barrel, said inner barrel having a proximal open end, comprising a conduit, and a distal open end where the inner barrel is slidably contained within the outer barrel causing the inner barrel to act as a piston where the conduit has a reduced cross sectional area relative to a respective cross sectional areas of the outer barrel and inner barrel, wherein a first fluid is located in the inner barrel, said first fluid extending only partially through the conduit such that the first fluid is separated from and not in contact with a second fluid, different to the first fluid and located in the outer barrel, but prevented from entering the conduit due to fluid mechanics; c. a second piston movable in and out of said inner barrel; d. a latching mechanism for locking and unlocking said second piston relative to said inner barrel, wherein said latching mechanism defines a path of movement for said second piston relative to said inner barrel such that when locked the latching mechanism is configured to maintain a volume of the inner barrel at a fixed volume when, in use, inner barrel moves within the outer barrel to expel the second fluid from the outer barrel the syringe being configured such that in use fluid mechanics retains the first fluid in the inner barrel during said movement of the inner barrel, and when unlocked the latching mechanism is configured such that in use movement of the second piston reduces the volume of the inner barrel to expel the first fluid from the inner barrel. a. an outer barrel with an open end; b. an inner barrel movable in and out of said outer barrel, said inner barrel having a proximal open end, comprising a conduit, and a distal open end where the inner barrel is slidably contained within the outer barrel causing the inner barrel to act as a piston where the conduit has a reduced cross sectional area relative to a respective cross sectional areas of the outer barrel and inner barrel, wherein a first fluid is located in the inner barrel, said first fluid extending only partially through the conduit such that the first fluid is separated from and not in contact with a second fluid, different to the first fluid and located in the outer barrel, but prevented from entering the conduit due to fluid mechanics; c. a second piston movable in and out of said inner barrel; d. a latching mechanism for locking and unlocking said second piston relative to said inner barrel, wherein said latching mechanism defines a path of movement for said second piston relative to said inner barrel such that when locked the latching mechanism is configured to maintain a volume of the inner barrel at a fixed volume when, in use, inner barrel moves within the outer barrel to expel the second fluid from the outer barrel the syringe being configured such that in use fluid mechanics retains the first fluid in the inner barrel during said movement of the inner barrel, and when unlocked the latching mechanism is configured such that in use movement of the second piston reduces the volume of the inner barrel to expel the first fluid from the inner barrel.