Feces are food residues passed after completion of travel through the digestive system.  Feces have a characteristic odor mainly due to skatole. Laboratories may be requested to test stains or other samples for the presence of feces, for example in the investigation of anal intercourse or where perpetrators have fouled a crime scene.  The screening of samples depends on the detection of urobilinogen, a bile pigment excreted in feces, which may be detected using its fluorescent reaction to Edelman's reagent. 

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