The invention relates to the field of purging systems for blood cell counters, particularly those having sensing zones including apertures of small dimensions. 
There are presently a number of methods for clearing debris which accumulates about the aperture of a blood cell counter.  One method involves providing a cleansing solution in the instrument in place of the sample solution, and running it through the system as one would during the counting operation.  This is fairly effective, but sufficient velocity of the cleansing stream may not be generated about the aperture to remove all debris, and the process is time consuming.  An additional problem is that the debris may be too large to pass through the aperture. 
Another method involves either the physical displacement or "flicking" of the aperture slide as described in commonly assigned U.S. Pat.  No.  3,783,376. 
Independent purging systems have also been employed where the previous sample is removed by a separate purge line rather than through the fluidic circuit normally used for counting.  A system which develops sufficient velocity in the area about the aperture to most effectively remove dirt and debris which could clog it has not previously been developed.