He has to permit anyone - in other words they're not really asking him permission. I read that sentence to mean that he doesn't actually have any say over who gets to use his blood.
Is there another source for this? Using phrases "has to" and "anyone" implies requirement.
In fact, the very next sentence is "This leaves Thomas dependent on other Rhnull donors", which re-enforces my reading of the previous line. If he could have a private stash, he would not be dependent on other donors.
Standing alone it's impossible to derive the true meaning; it's the perfect doppelganger.
Based on the subsequent sentence I decided the author was in fact claiming that he couldn't save blood for his own exclusive use, but then immediately thought that can't possibly be true.
Poor machines will never learn to speak this language!
Fairly sure he's reading it correctly - the article goes on to talk about how he has to depend on other donors, and how he has to be very careful since there aren't any nearby.
The sentence by itself is unclear, but the context of the surrounding paragraph makes it pretty clear that while he can donate blood to have on reserve in case he needs it, he might be screwed if someone else needed it, because he has to allow them to use it.
