From Aristotle’s “Problems,” Book VII - Problems Arising from Sympathy, Number 4: Why do those who get too close become infected by certain diseases, whereas no one becomes healthy from contact with health? is it because disease is motion, whereas health is rest? Therefore, the one moves, but the other does not. Or is it because the one occurs involuntarily, the other voluntarily? And what is involuntary differs from what is voluntary and what is due to forethought.