[Solved] Combining direct-mail lists is called merging,and deleting the repeat names is called purging. Bilirubin: A yellow breakdown product of normal heme catabolism. Its levels are elevated in certain diseases, and it is responsible for the yellow color of bruises and the brown color of feces. Ammonia: A colorless gas with a distinct sharp smell, commonly used in cleaning products and as a fertilizer, and also produced naturally in the human body. Bacteria: Microscopic, single-celled organisms found everywhere in the environment, which can be either beneficial or harmful to humans and other living beings. Occult Blood: Blood not visible to the naked eye, often detected in stool or urine samples to diagnose conditions such as gastrointestinal bleeding.