Scans_Daily

But my point is that he WOULDN'T be changing his eating habits - going by this hypothesis, vampires suck blood because the lifeforce is IN the blood. In this case, though, Jono HAS no blood, or at least not a normally functional circulatory system, so his lifeforce isn't in it - it's manifesting in a more concentrated form than usual as the energy that keeps him alive. If Dracula fed on Jono, he would still be sucking out the lifeforce like he's been doing for centuries - it's just that said lifeforce would be PURE lifeforce, without being mixed with blood.
And I'll grant you that the writer probably didn't write the story with all these background details in mind - this is just my own attempt to explain Dracula's actions. If I'd written Marvel a letter at the time, I'll bet I would've gotten a No-Prize.