of the invention functions to selectively align one of the inlets of the radially extending flow control channels of the selector knob with a selected one of the spaced apart micro rate fluid outlets 166 a 166 b 166 c 166 d and 166 e of the rate control cover 162 fig1 also forming a part of the flow control means of this latest form of the invention is a macro rate selector knob 190 that is carried within a horizontal bore 192 formed in housing portion 604 b selector knob 190 is also of identical construction and operation to selector knob 190 as described in connection with the first embodiment of the invention and is uniquely provided with a plurality of radially extending flow control channels 194 a 194 b 194 c 194 d and 194 e each having an inlet port and an outlet port which it is in fluid communication with an axially extending passageway 196 axially extending passageway 196 is in turn in fluid communication with administration line 148 selector knob 190 which also comprises a part of the selector means of this latest form of the invention functions to selectively align one of the inlets of the radially extending flow control channels of the macro selector knob with a selected one of.