Abstract: Tissue specimen treatment apparatus of the multi-chamber type having a plurality of containers, for instance arranged in a circle, and means for transporting a specimen for treatment to selected such chambers in a prescribed sequence, is characterized by a containment vessel disposed about at least the open tops of the containers and by cover means movable with the transporting means and evelosing the interior of the containment vessel so as to separate the specimen from the ambient atmosphere. The cover means preferably closely overlies the open tops of the containers to minimize the volume of the containment vessel, and is formed with a small volume transfer enclosure to receive a specimen during transport. The cover may have a close fit to the containment vessel, sufficient to restrict exchange of gases etc. between the external atmosphere and the containment vessel, or more positive sealing arrangements may be provided--e.g.