Microscope cover glass is a very thin square piece of glass that is placed over a drop of liquid on a microscope slide
Because of surface tension
the liquid drop alone tends to sit in a thick dome
With a cover glass in place
the drop is flattened out
allowing the clinician to focus with high power very close to the specimen
The cover glass also confines the specimen to a single plane which reduces the amount of focusing necessary
The cover glass also protects the objective lens from immersion into the liquid
