. . . "The discharge line 20, the drip chamber 18, the drip tube 16, the valves 22 and 23, and the two hose lines 11 and 12 can be constructed as disposable parts which can be simply replaced when the device, i.e. the parts to be reused, such as in particular light barrier 30, CPU and RAM, are to be used for example in another operation." . .