In most human societies, ritualized and firm rules evolved for cutting the navel-string and handling the umbilical stump. These customs were not always beneficial, and contributed to umbilical infection, neonatal tetanus, and navel hernia. After prematurity, neonatal tetanus was the most frequent cause of death in poor countries up to the 19th century. It was caused by poor cord hygiene and by the age-old habit of severing the navel-string with biological products instead of man-made tools, which included palm leaves, blades of grass, mussel shells, crusts of bread, and other devices likely to be contaminated with tetanus spores. The navel-stump was covered with zinc powder, starch, oak-gall powder, grease, musk, clarified butter, and many other substances believed to protect the baby from evil, but actually creating anaerobic conditions in the umbilical wound. Care of the cord was associated with deep-rooted rituals and customs, and dangerous techniques persisted on islands well into modern times.