Vitae

Vitae
Vitae or "blood energy" is what a vampire needs in order to survive. When a vampire drinks a human's blood, they use the energy inside of the blood. This is what vitae is. The blood is pumped around the Vampires body only using two Organs - The Brain and the Heart, meaning that any other Organ to a Vampire is useless. This is because Vampires are undead, meaning they have no living cells - hence no other Organ is needed. Because Vampire cells are dead, every movement that a Vampire does requires vitae, whether it be concious or subconcious. The fact that vampires use the very essence of a human being, their "energy" to survive, means that a Vampire has 100% accsess to their brain. This accsess is the is what gives Vampires the capability to use Vitae for magicks.

Vitae in regard to Torpor.
A Vampire will enter a state known as "Torpor" when she/he has too little Vitae in their body. Torpor could be described as a Coma, the mind shutting down due to the lack of Vitae to run it. If we go back to the earlier state point of Vampires having 100% accsess to their brain, if not enough Vitae is given to fuel such a high accsess point; this is when a Vampire Torpors.

Gaining Vitae
To gain Vitae, a Vampire must feed off a living human. Only human blood contains this energy that fuels a vampire; meaning Vampires cannot feed of animals, other Vampires, or Lycans. The blood does not have to be fresh, but it does have to taken from a living person; dead blood does not contain the living energy of Vitae, rendering it useless.