Differentiating between early melanomas and melanocytic nevi: A state of the art review ScienceDirect The Quantity of Blood Required to Produce a Tarry Stool. How much? Melena, characterized by black tarry stools, can occur with as little as 50 cc of blood in the stomach. How Melanocytic Nevus: What Is It, Causes, Signs and Symptoms, and More Osmosis Melanocytic nevi and malignant melanoma Medizinonline Melanin Definition, Types & Function Lesson Study.com GASTROINTESTINAL HEMORRHAGE (2): Melena. Melena, the passage of black, tarry stools, usually implies blood loss greater than 500 ml originating anywhere between the oropharynx and the right hemicolon. Melena occurs most often,