I have a question about Horcruxes.
Actually, I have several, but just this one for now (story spoilers, you know;)):
If someone had split their soul and lost a bit of it to a Horcrux, would the Healers at St. Mungo's be able to tell?
Interesting question, yes? What do you think? I'm inclined to say 'no', since it seems very inexact, but that may be because that's just how I want it to work for the plot bunny I've been nursing for months and months.
Since there is really no way to measure a soul, (you can't see, smell, hear, feel, weigh....it. Many people don't even believe they exist.) I'd say no. Granted, wizards obviously have ways of 'handling' them, since they have invented Horcruxes in the first place, but even when Harry destroys them, he wouldn't really have known what it was if Dumbledore hadn't first told him. For example, when he destroyed the part in the diary, it bled ink, but Harry had no idea he'd killed a bit of soul, much less how much soul or how much had been left in the creator of the Horcrux. And they all behaved differently so it seemed as though they were merely powerfully cursed items. *hopes that made any sense at all* *needs to go to bed*
Also, Horcruxes are rather secret and few people even know about the magic, as we learn in the part about Slughorn's memory, so it is even more unlikely that a Healer would even consider trying to figure that out. I have to doubt that Horcruxes are taught in routine Healer training, or I don't think Slughorn would have been so keen to keep the memory secret.
From Voldemort's appearance, it does seem that the evil in the magic has a physical effect, but that was after seven Horcruxes. I don't know if only one would cause any noticeable visible side effects to give a Healer hints. So yeah, in my rambling way, I'd say no to your question. :o
Just to add to what moonymaniac said:
Slughorn told Riddle that Horcruxes were very dark magic, and Hogwarts doesn't teach dark magic. Since the Healers at St. Mungo's most likely attented Hogwarts, they would never have heard or read about it as Hogwarts' library didn't hold books on the topic. Dumbledore knew about the Horcruxes cause he looked for possibilities to destroy Voldemort. Slughorn might have known because he was interested in the topic purely out of scientific reasons, so he was able to tell Riddle when he pressed. But your general healer wouldn't know, so no to your question.
I agree that the Healers would not know of Horcruxes in particular, but they may notice that something was off. After all, they're healers, so they'd be more attuned to what a fully-souled person was like in a lot of different ways. There's likely to be things that are lacking or not working the way a normal person's would. Maybe, if it was a Healer with a Prejudice, they'd think the person wasn't a full wizard (i.e. linking the soul to the ability to do magic, which, of course, is completely unrelated) -- maybe a Squib who actually managed to get something out of the Quik Spell course or something. I definitely think they'd notice something odd, but I don't know that they would know what it was. And being scientists, they'd do everything they could to find out what it was. And they might not stumble onto Horcruxes, but they might stumble onto something else about souls, which would lead them to understand what the basic problem was (missing part of soul) without knowing the specific cause (Horcrux). Then, they'd probably look for ways to rejoin the soul, which might involve looking for what might cause a soul to be split . . . and depending on how persistent they were, they might find something on Horcruxes.
But let's say the healers have never before seen that person. How are they to know that s/he missed something of his/her soul? Voldemort split parts of his soul off "regularly", and still no one noticed something. He continued behaving "normally" - or as normal as anyone as "deranged" as him would.
So why would someone else behave differently, and how would the healers notice that if they do not know the person in the first place?
This is all very much what I was thinking - that the Healers would not be able to recognize something so inexact as a bit of soul missing from a person. That is not to say that someone far more talented than me could convincingly write such a thing, but I'd think it would be an exceptional Healer in an exceptional situation who would figure it out.
Good point about Healers probably not studying it much. I imagine they undergo advanced training after Hogwarts, and that would include studying Dark magic, but it does sound like Horcruxes are quite rare, and that it would be highly unlikely to be included in any sort of study, particularly since the soul is such an inexact thing.
Of course, the physical effects might be a clue, but it would depend on how many Horcruxes, I suppose. Voldemort had so many it changed him dramatically. One Horcrux might not be that noticeable.
All right, one potential plot hole plugged! ;)