Abstract: An inlet chamber is connected to a nozzle section by way of a plurality of tubes. Diluting liquid for mixing with paper stock flowing through one or each of said tubes is fed into the tube via annular inlet means. To ensure thorough mixing, channel means leading into the annular inlet means is configured to create turbulent flow of diluting liquid prior to its introduction into the tube, for example, by consisting of a helical or spiral duct, or by being provided internally with baffle means.