An apparatus for locating and venting pathogen cells in blood. A cassette has a plurality of thin holding chambers that are filled with blood drawn from a patient. A light source illuminates each of the holding chambers and passes light to an underlying sensor array such that the cells in the blood produce shadow images of the cells in the sensor array. A processor performs pattern recognition to identify and locate the pathogen cells by use of an image library. After the pathogen cells are located, a pump is operated to move the identified cells to a processing zone. When each identified cell reaches the processing zone, a control voltage is generated to open a valve to vent the identified pathogen cells. The pump refills the cassette holding chambers, returns the processed blood to the patient, and the procedure is repeated for a treatment time period.