"It's not hard for witches who focus on magic - like me - to invent variants on spells that have been done, like when I brought the alethiometer I based the design on another summoning-an-object spell. But completely new things are harder. We have spells to cure diseases - witches get attached to mortals more than often enough to encourage that - but there's nothing for me to start from for boosting immune function unless it's brand-new and hasn't made it into my clan library yet."