Abstract: The invention provides an injection device comprising an open cavity, an injection needle projecting from the bottom of this cavity, a first leakproof compartment delimited by a first section of a mobile barrier, first devices for displacing the said first section of a mobile barrier to vary the volume of the compartment, at least one passage communicating between the said first leakproof compartment and the said cavity, a second leakproof compartment for a product to be injected, delimited by a second section of a mobile barrier, and second devices for displacing the said second section of a mobile barrier to vary the volume of the compartment. The said first and second leakproof compartments extend longitudinally within a tubular body. The cavity is located at one end of this tubular body, while the said first and second devices for displacing the said first and second sections of a mobile barrier are accessible at the other end of the said tubular body.