Would you like to find out? A blood sample and a spell and I could tell you how much of your blood is demon blood.

[ He does not actually remember how much demon blood the Jace from his world was given. He thinks none? Ithuriel was involved, and he's relatively sure the one raised with demon blood was the other child, Sebastian or Jonathan.

Either way, Ragnor doesn't like the assumption that demon blood necessarily corrupts. ]