Abstract: The electrical sensing circuitry includes a power supply and a signal-detecting circuit which are coupled through the resistance of an electrolyte in a liquid in an aperture of a particle-analyzing device between sensing electrodes positioned on either side of the aperture. The liquid containing an electrolyte and the passage of a liquidborne particle through the aperture causes a change in the resistance of the aperture thereby generating a signal which is detected by the signal-detecting circuit. The parameters of the circuit elements are chosen to provide circuit relationships which render the particle-generated signal independent of the diameter of the aperture. This is achieved by utilizing a power source having a low output impedance and a signal-detecting circuit which has a low input impedance for both D.C. and A.C., namely, at the signal frequencies of the signals sensed.