Filtration system and method for obtaining a cytology layer

A filter assembly for separating and collecting a layer of particulate matter from a liquid containing the particulate matter, the filter assembly comprising:

• a holder having a base and a surrounding sidewall projecting from the base, the base and the sidewall defining an open cavity extending from the base to the rim of the sidewall at the distal end thereof;
• an inner fluid pervious medium in the cavity having opposed inner and outer faces, the inner face facing the base;
• a flow opening in the holder in fluid communication with the inner face of the inner fluid pervious medium;
• and
• an outer fluid pervious medium overlying the outer face of the inner fluid pervious medium and attached to the sidewall, the exposed face of the outer fluid pervious medium adapted to collect a layer of the particulate matter, the inner fluid pervious medium being of low fluidic impedance relative to the outer fluid pervious medium so that the pressure drop across the inner fluid pervious medium is less than the pressure drop across the outer fluid pervious medium when liquid flows therethrough.