microprocessor 29 as instructed by the six switches the injection of local anesthetic into a patient it will be understood that a pressure transducer in the form of a piezo electric crystal device or other electronic device can be substituted for the springs 40 and 41 to actuate the switch 34 the pressure transducer is inserted between the motor 28 and a fixed frame piece to provide outputs reflecting the intermediate pressure of approximately 7 to 12 pounds and the high pressure of approximately 27 to 45 pounds because unlike springs there is very little if any perceptible translational motion involved in the actuation of such pressure transducers a third output is provided so that the motor can be turned on again after a predetermined drop of approximately 2 to 5 pounds as will be described below in reference to fig7 a and 7b in the illustrated embodiment of the invention the screw pitch of the plunger 2 and the internal driving collar of the stepper motor 2 are selected so that for each step of rotation of the stepper motor the plunger moves 0 0005 inches the microprocessor is programmed to step the motor at successively increasing rates to generate the flow rate curve of fig6 in the first second step.