rod application_number US 37845389 A description fig1 is illustrative of a piece of present day laboratory equipment which includes a syringe s for putting liquid into and taking it out of a petri dish d or a series of petri dishes which are positioned one behind the other into the plane of the figure the syringe is clamped to an anti backlash nut n and moves upwardly and downwardly as a lead screw ls is rotated by a motor m the clamp c which attaches the anti backlash nut to the syringe may be independent of or a movable part of a frame f that supports the motor m for example a link l may be mounted in a guide g to prevent the syringe from rotating the frame f moves linearly in a direction into and out of the plane of the figure in a track t the lower end of the lead screw ls is journaled in a bearing b also in a track t the frame f and the bearing b move in a direction toward and away from the viewer so that the syringe can sequentially add or remove liquid from a series of petri dishes d or test tubes by use of apparatus made in accordance with the.