Disclosed is a method and apparatus for manipulating fluids. The apparatus may include a microfluidic structure including inlet channels (1 and 2) and outlet channels (306, 307, 308, 309, 310, 311, 312, 313, and 314) oriented among bifurcated (5), trifurcated (6) and merging junctions (7 and 8). The apparatus splits and merges fluids flowing in the channels to produce successive dilutions of the fluids within the outlet channels. Multiple apparatus may be combined in serial, parallel, combined serial and parallel and/or stacked configurations. One or more apparatus may be used alone or to provide various devices or chambers with the diluted fluids.