carts 10 located in second compartment 24 to platform 30 these transfer means comprise two drawers 42 each of these drawers 42 receives two carts 10 a drawer 42 is clearly seen for example on fig1 to 13 each drawer 42 has a horizontal bottom 44 and three vertical side walls one side wall called central side wall 46 extends vertically in a plane perpendicular to the front face of second compartment 24 and is more or less at the center of second compartment 24 when each drawer 42 receives a set of two carts 10 the two central side walls 46 corresponding to the two drawers 42 each time are between the two sets of two carts 10 in the embodiment shown on the drawings it has been chosen to use two electric motors 48 to drive each drawer 42 on the figures two power plants are seen each of the plants shown containing two electric motors 48 for each drawer 42 a first electric motor 48 is integral with unit 20 or more generally with second compartment 24 while second electric motor 48 is integral with platform 30 each electric motor 48 drives by means of a shaft 50 two cogwheels 52 each installed on shaft 50 at a distance from one another each of these cogwheels 52 cooperates with a rack 54 fastened horizontally onto a central side wall 46 as for shaft 50 bearing the two cogwheels 52 it extends vertically in this way when two cogwheels 52 of a shaft 50 each meshed with a rack 54 are driven in rotation by a corresponding electric motor 48 corresponding central side wall 46 is driven in translation along a horizontal direction.