This month's lesson will lay out the dark magic-induced injuries and illnesses a healer may have to treat at some point in their career. Usually there is no special strategy for dealing with dark magic, as a lot (but not all) of it comes under the banner of 'ordinary' magic applied with evil intent. As a result, this lesson will be a mixture of various disciplines and approaches.
Potions
Many potions may be used by a dark witch or wizard to cause harm to another person, and we have briefly covered these in other lessons. Main examples include the Draught of the Living Death, brewed with asphodel and wormwood;, and poisonous potions containing large volumes of things like belladonna or other harmful substances. Even simple potions like sleeping draughts, confusing concoctions and shrinking solutions, if given with malicious intent, can be tools of the dark witch or wizard.
The most essential ingredient in a healer's cupboard to safeguard against lasting damage or death from such potions is a bezoar. This can be swallowed by the victim and will neutralise any poison in the body. If a bezoar is not available, an antidote must be brewed, but this is a long, complex process, requiring that you have a sample of the harmful potion and time to deconstruct it into its individual ingredients in order to formulate your remedy. Needless to say, there is not always time or opportunity in urgent situations to do this, and it may be a good idea to have a well-stocked cabinet of pre-prepared antidotes to the more common harmful potions.
Spells
The most obvious spells one thinks of in connection with the dark arts are of course the three unforgivable curses. Cruciatus - the pain curse; imperius - the control curse; and avada kedavra - the killing curse. For the former two curses, a witch or wizard with sufficient power will be able to cure the victim with 'finite incantatem', followed by bed rest, hot chocolate and sleeping draughts if required. Unfortunately for the latter curse, there is no shield from it and no way of reversing it.
Other, less deadly spells, include jinxes and hexes that damage or interfere with the victim's body or mind, such as the confundus charm, babbling curses, memory charms, petrification hexes, taratallegra or the jelly-legs jinx, densaugeo, the leg-locker curse, and many more. The milder jinxes and hexes are often used as a means to an end in duels, where the attacker wishes to distract and weaken the victim, perhaps to gain an advantage. Many of these can be treated with a simple 'finite incantatem' and/or appropriate healing care for any physical effects.
Transfigurations are more difficult - as with any transfiguration, one performed by a dark witch or wizard to attack someone can be reversed with thorough, careful attention to your patient while reversing the process step-by-step. It is useful to note that dark magic transfigurations are generally easier to reverse than accidental ones - although the spell itself tends to be more powerful, the victim is usually transfigured in a much more precise and orderly fashion than if the spell was cast in anger or had simply gone wrong.
Creatures
There are a number of 'sentient' (i.e. it's got enough brains to know it's doing wrong and should know better but does it anyway) creatures that are associated with dark magic and that actively seek to harm.
Chief among these, because of their numbers, is the werewolf. Many werewolves seek to limit the amount of damage they do at the full moon by taking the wolfsbane potion to subdue themselves, but there are a great number who revel in their aggressive natures at that time of the month, and actively seek out victims to bite. A werewolf bite cannot be healed magically - you must make your patient as comfortable as possible, and keep the wound clean while it heals. Since a werewolf bite has lasting effects more dangerous than a scar, werewolves are considered the greatest threat out of all dark-magic-associated creatures.
Trolls and giants are also malicious towards humans, and can obviously cause a great deal of physical harm. Luckily, wounds inflicted by these creatures are not resistant to magical healing, and can be dealt with in the usual way.
Basilisks, although not 'intelligent', as such (but then, can trolls and giants be said to be intelligent?), can also be considered in this category, since they are only ever associated with dark magic. While you will not be able to help anyone who's been eyeball to eyeball with a basilisk, you may rarely be required to attend to someone who's been bitten by one. The venom of a basilisk, if not neutralised in time, is invariably fatal. This is one of the rare cases in which phoenix tears are the standard treatment - application of tears to the wound will almost always inactivate the venom and repair all tissue damage sustained in the attack. A bezoar is also helpful, but to counteract the venom of an adult basilisk, it had better be a pretty big one. Depending on the basilisk, of course, not even phoenix tears may work, as we see in the case of Arthur Weasley, where nothing apart from blood-replenishing potions and time seem to have any effect on his condition. We can only assume that Nagini, the basilisk that bit him, was more powerful than the normal run-of the mill dirty great snake, since it belongs to Voldemort himself.