Abstract: A method for treating a human or animal cell sample (4) arranged on a slide (2) comprises dispensing treatment liquid onto the slide between the sample and the leading edge (5) of a cover tile (1) having a recess or cavity (6). The leading edge is bevelled and has an opening (13) into the cavity. Once dispensing is completed the method involves moving the tile over the slide to trap the liquid in the cavity. A small volume of sealing liquid in the form of evaporation inhibitor liquid, preferably mineral oil, is then applied to the slide preferably at the leading and trailing edges of the tile in a manner causing the evaporation inhibitor liquid to wick around the entire perimeter of the tile to form an airtight seal between the tile and slide around the cavity.