At least four infants have died and over 50,000 are sick in China after melamine was added to liquid milk. Melamine is an industrial chemical. It contains a lot of nitrogen, so during chemical analysis it raises the apparent protein content of foods and allows the producer to slack off on food-grade protein. It’s not particularly poisonous, but high amounts of nitrogen make the kidneys work harder. It can also precipitate out into sharp crystals that cause permanent kidney damage. And that is deadly.