There should be no snot on the nostrils… A peasant wipes his nose on his cap and coat, a sausage maker on his arm and elbow. It does not show much more propriety to use one’s hand and then wipe it on one’s clothing. It is more decent to take up the snot in a cloth, preferably while turning away. If when blowing the nose with two fingers something falls to the ground, it must be immediately trodden away with the foot. The same applies to spittle.
Thus Norbert Elias’ The Civilizing Process summarises some instructions in Erasmus’ 1530 publication On Civility in Boys. This post compares The Civilizing Process with Steven Pinker’s The Better Angels of Our Nature to ask: are we civilised, and is civilisation what we want?