ADHESIVE LABELS. — It cannot be too generally known that the very numerous cases of cancer which have lately prevailed are attributed by the faculty and scientific men to moistening the adhesive postage stamps with the tongue and lips. A little new milk is much preferable, and also causes them to stick faster particularly on glazed and smooth letter paper.
Waterford Chronicle 19 December 1840
Not a lot of people know that.
Irish waterways history 