On Appetite
We see it all the time; a woman walking home from work decides to take a shortcut through a dark alley. A shadow flickers past her, she stops—looks around—nothing. She continues walking, though at a faster pace. Just then a flash of movement, a cry for help, a muffled scream, and it’s all over.
The detective arrives at the scene, “What’s the story?”, he asks.
The coroner, still kneeling over the woman’s (now pale) body, speaks.
“She’s been completely drained of blood.”
But there isn’t a trace.
The average human body contains around 5 litres of blood, closer to 4.7 for our female vic over there. Now whether or not the vampire responsible, sucked, sipped, or lapped up the blood from the holes in her neck (which is a topic for another post all together), we assume that he ingested all of it.
Problem is, the human stomach can only hold an absolute max of ~4 litres.
After ~40% of blood loss a person will go into shock and die without treatment, so two litres of blood sucking would be enough to fill a vampire’s stomach and kill its victim.
On to another issue.
As far as I know, no data has been collected as to exactly how the supernatural digestion of blood occurs within a vampire. Or why some vampires seem to be constantly feeding, whether you’ve got an insatiable blood lust or not, if your stomach is literally completely filled, as shown above, by one meal then why do we see in some cases a string of deaths overnight?
Hypothesis
Since we know that, to a vampire, blood is life, and that blood is compromised of very few ingredients (see the Constitution of Normal Blood chart to the left of this page), we can reasonably make the conclusion that very little (or no) digestion is necessary, making the stomach less the part of a biological process and more like just a receptacle for blood.
Now, as we can see in this diagram from wikipedia, the stomach is supplied with blood through two arteries and sits right next to the aorta. If we imagine that one of the physical changes a human undergoes during the transformation into a soulless creature of the night, is that the blood flow to the stomach from the heart reverses. This would allow freshly consumed blood to immediately exit the stomach and flow through the heart and body; and, ipso facto, account for the insatiable blood lust.
