Sheaths for jointed instruments

A surgical apparatus, comprising:

• a surgical instrument having a shaft, a joint, and an end effector coupled in series;
• one or more openings on the shaft, in the joint, or both on the shaft and in the joint, the one or more openings providing flow communication between an exterior of the shaft and an interior of the shaft;
• a sheath having a hollow body including a first portion and a second portion, the sheath being in an operable position on the surgical instrument so as to prevent infiltration of biological material through the one or more openings by the first portion covering the shaft and the second portion covering the joint on a condition that the one or more openings are on the shaft, the one or more openings are in the joint, or the one or more openings are on the shaft and in the joint;
• wherein the sheath is removably engaged with the shaft of the surgical instrument to retain the sheath in the operable position on the surgical instrument and to permit removal of the sheath from the surgical instrument;
• and
• wherein the second portion of the hollow body is made of flexible porous material, the flexible porous material having a pore structure providing a barrier to passage of liquids and enabling the second portion of the hollow body to substantially retain its cross-sectional shape or diameter when in a bent configuration, the flexible porous material comprising a colorant.