What is the function of blood in a vampire's bloodstream?

So… Daybreakers it was with a bag of potato chips.

With visuals reminiscent of Blade Runner and The Matrix, it’s the perfect stage to tell a blood-curdling futuristic vampire tale. Daybreakers is set in 2019 when vampires have taken over the world. They control business, big and small. They walk the streets freely (at night, of course). And, if it’s necessary for them to be outdoors during the day, advanced technology has allowed them the luxury of owning and riding in vehicles capable of blocking the sunlight completely. The only imperfection in their perfect lives? Shortage in the supply of human blood.

Humans, a species dwindling fast, are hunted to serve as lab rats in a frenzied race to develop a substitute for blood to keep the vampires fed. Otherwise, they turn into “subsiders” — vampires still in human form but who have developed bat-like wings and whose skin is so taut and withered that they look like winged corpses.

Edward Dalton (Ethan Hawke) is the lead hematologist in a corporation that is the largest supplier of human blood in the United States. He and his partner are in the last stages of testing a human blood substitute. As a volunteer (a vampire, of course) is injected with the substitute, his body explodes in a bloody mess.

My daughter and I looked at each other. I forget now who asked the question first — do vampires even have blood? As if on cue, my mind looked back on Bram Stoker’s Dracula, both book and film, and tried to recall if vampires bled when stakes were driven through the heart. I just saw a film clip of Dracula on Youtube. Not only did Lucy Westenra bleed when the stake went through her heart and her head cut off — she even spewed blood on Van Helsing when he put a cross next to her face.

The blood-spewing did not happen in the book but, yes, she did bleed when the stake was hammered into her chest by her betrothed, Arthur. From Chapter XVI:

The Thing in the coffin writhed; and a hideous, blood-curdling screech came from the opened red lips. The body shook and quivered and twisted in wild contortions; the sharp white teeth champed together till the lips were cut, and the mouth was smeared with a crimson foam. But Arthur never faltered. He looked like a figure of Thor as his untrembling arm rose and fell, driving deeper and deeper the mercy-bearing stake, whilst the blood from the pierced heart welled and spurted up around it. His face was set, and high duty seemed to shine through it; the sight of it gave us courage so that our voices seemed to ring through the little vault.

And then the writhing and quivering of the body became less, and the teeth seemed to champ, and the face to quiver. Finally it lay still. The terrible task was over.

But Bram Stoker did not invent the vampire. Centuries before he wrote Dracula, vampires were already in the folklore of various cultures. The 12th-century English historian William of Newbergh wrote about corpses rising from the graves but blood-sucking was not mentioned. There is reference to a 16th century rabbi who told a story about a woman possessed by a vampire-like demon. Seventeen years before Dracula was published, Sir Richard R. Burton (no, not the actor) published Vikram and The Vampire, a collection of eleven vampire stories translated into English from Hindu sources.

So, Bram Stoker just personalized everything by giving one vampire a name and weaving a story around him. If Bram Stoker’s vampires bled, is it because the author patterned their characteristics on existing folklore? Sadly, I am unable to find any reference to answer that question. And the lack of answer raises even more questions:

1. Vampires are undead, their hearts don’t beat, so, if there is blood in their veins, what is its function? Since it is the brain that regulates appetite, and vampires do hunger for human blood, can we assume that the blood in their bloodstreams circulate through the brain to trigger pangs of hunger?

2. Vampires are undead, they do not process food that way living creatures do, so, what happens to the blood they drink? Does it become pee or poop (unlikely) or does it somehow end up in the creatures’ bloodstreams?

3. Vampires are undead, their flesh is cold and pale, so, if they have blood which apparently stays in liquid state, how does it stay liquid unless it were warm (we do know that blood congeals when it turns cold)? If the blood were liquid and warm, why should their flesh be cold and pale?

Nothing makes sense, does it? But then again, vampires are mythical creatures, and myth defies logic. Why try to find logic at all? We should just enjoy the stories — the good ones, at least, like Bram Stoker’s Dracula. And Daybreakers? Hmmmm… it’s watchable.