Zevachim 19 - Clothes of a Kohen
A Kohen who has wounded his finger on Shabbat may wrap reed-grass over it if he is in the Temple, where the Sages did not enact additional prohibitions that would complicate the service, but not outside, where one is not allowed to cure non-threatening conditions on Shabbat.
For a Kohen, a small bandage around a wound is forbidden, because it constitutes an extra garment. Another opinion is that an extra garment is only important in the place of garments, or on the right hand, which is used for service.
Rava asked a series of questions. If the wind entered the Kohen's garment, does this invalidate the service because the garment is not "on his body," or is it a normal manner of wearing? Does a louse constitute interposition between the kohen's body and the garment? The dead one certainly does, but what about a live one? Since it comes and goes, it is like a growth on his body, or, since he does not like it, it is an interposition? What about the dust of the earth, a hand in his bosom, or thread hanging from the garment?
Art: Peeter Franchoys - Ruby on the Fingernail