How is it that Knives can heal himself when Vash can't?

[vash0147]

I know at one point Knives was using a rejuvenation tube from the SEED ship but in an episode when Vash and Knives are talking Knives said that Vash can't heal himself because of something about the people i don't quite remember but Knives said that Vash can't heal himself because of how Vash treats the human race. Sorry if its a little vague i'm not the best writer in the world in fact i failed english almost everytime in high school.

[WhoWantsToKnow]

What Knives is saying is that Vash is disregarding his own abilities so as to be more like the humans. As Knives says, "You're not a human being. You're a plant." Vash hasn't had the kind of access Knives does (because he's been with the humans all this time), so his body doesn't get a chance to rejuvenate the way Knives' body does--thus the scarring.

[vash0147]

Thank you

[Trigun Forever]

That's sort of it. Vash wants to be human, so he doesn't use his godlike powers unless he is preventing bloodshed. Knives recklessly uses his power. When a plant's hair turns black, they die. The hair darkens as they use more power. Knives had more power, hence the lighter hair. Vash used his power to protect people. Hence, their hair darkened. Knives didn't die yet or get weakened farther than Vash because he had more power to start with, which is why Vash couldn't overpower him on the spaceship or on the planet after the crash or in the 3rd city of July after the death of Rem's descendant.

That's just my theory though