Bleeding, also known as a hemorrhage, haemorrhage, or simply blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vagina or anus, or through a wound in the skin. Hypovolemia is a massive decrease in blood volume, and death by excessive loss of blood is referred to as exsanguination. Typically, a healthy person can endure a loss of 10–15% of the total blood volume without serious medical difficulties (by comparison, blood donation typically takes 8–10% of the donor's blood volume). The stopping or controlling of bleeding is called hemostasis and is an important part of both first aid and surgery. The use of cyanoacrylate glue to prevent bleeding and seal battle wounds was designed and first used in the Vietnam War. Today many medical treatments use a medical version of "super glue" instead of using traditional stitches used for small wounds that need to be closed at the skin level.