This is a versatile discrete monostable circuit. This circuit consist of 2N3819 JFET and 2N3704 transistors. This monostable multivibrator circuit  has additional input to enable or inhibit the function at any time without causing output pulse. The input of this circuit accept a standard digital IC voltage levels. Here is the schematic diagram of the circuit:

Versatile Mono circuit schematic

The  output’s timing cycle begins when the logic at  input B changes to high. This low to high transition produce a small pulse that activate the Q3, shorting briefly the collector of Q2 to ground  through Q1 to activate the output and start the timing. If A input is low then the path from Q3 to ground will be broken, and this condition will inhibit the circuit to get triggered. This mechanism provide the inhibit or enable-disable mechanism without triggering the circuit. [Circuit’s schematic diagram source: R. Tenny]