MENSTRUUM is any liquor that serves for the extracting of the essence of anything.(The Art of Distillation of John French)
The Science of Menstra is ONE BIG BASIS that's one should know imperatively if one want to do anything in Spagery, Archemy or Alchemy. Otherwise, nothing can happen !
A Menstrum can be dry or wet, composed of volatile part, or fixe part, it can be entirely fixe, or entirely volatile, it can be deliquescent, or not. It can be easely made, or extracted, or with a lot of work. It can be an alcaline substance, or it can be an acid substance. It can even, by time, extract his own sulfur !
With that you can Ex-tract, pull out of the body, its blood, its force, its oil, its sulfury part, the Soul. This is the vampire, blood sucker.
A menstrum can be mineral/metallic, from salts, from vegetables, or animals/humans. They all have their forces and weakness.
A mentrum is a key to unlock the doors of matter. It is a very great thing indeed, because you can make wonders with it.