Abstract: Apparatus for introducing fluids into, and withdrawing fluids from, a hollow organ of the body, in particular a galibladder, for conducting litholysis, comprises a piston-type injection device having a multi-directional valve and which can be removably inserted into an operating mechanism. The injection device has a chamber located in front of its piston and serving as a settling chamber for a mixture of organ secretion and stone sludge removed with the solvent from the hollow organ. The valve is for the sequential connection of the pressure chamber to the hollow organ, to a tank for the solvent, and to a receiving vessel for fluid drawn off.