[The following is an excerpt from an old 100-level Biology textbook lying around Yugi and Joey's apartment, the ownership of which remains a mystery]
Despite their constant presence in modern society, there are many myths about vampires that have yet to be fully dispelled. Chief among them is the idea that vampires are undead. While it is true that vampires enter death-like state once the vampiric infection enters the body, the common belief that they are no longer physically alive was scientifically disproven in the early 20th century when advances in medical technology made it possible to detect a vampire's heartbeat. The changes which the vampiric infection introduces to the human body include increased strength and durability of the musculoskeletal system, heightened reflexes, enhanced senses of sight, smell, taste and hearing, a boosted immune system, and an extremely fast cellular regeneration rate. It is this last quality which makes it seem like vampires are 'frozen' at the age when they were first infected; their bodies are constantly healing themselves, the minute damages of age and wear healing flawlessly within nanoseconds. Since their boosted immune system prevents them from contracting illnesses, barring malice or accidents vampires are functionally immortal.
This fast healing rate, however, gives rise to their need to consume human blood. Like any other living beings, vampires need blood in their veins, distributing nutrients and oxygen throughout their cells. However, their boosted regenerative capacity is extremely demanding on the metabolism and as a result, unlike any other species, it is entirely possible for vampires to naturally run out of blood. The exact process by which vampires convert the blood they consume into blood compatible with their bodies regardless of type or genetic differences, as well as the near-direct way the new blood cells pass into the bloodstream, is not yet fully understood. However, the dire consequences of a vampire failing to feed at least once per month are well known. Blood withdrawal at first presents as progressively severe anaemia, escalating to show symptoms characteristic of starvation, dehydration, and anoxia. If a vampire does not feed within two weeks of when they begin to show signs of blood withdrawal, the condition will result in death.
A/N: Yes, it's an update already, but this and Chapter One were supposed to have been posted at the same time as the Prologue...note to self: make sure ALL of ff . net is working before posting new stories...*grumble grumble*
This is just a quick heads-up on what constitutes a vampire in this 'verse, because there was no way to fit this into the story proper without it sounding forced but it needed to be said. Don't worry, this is the only exposition-dump-entry.
