The histological slide is a rectangular glass slide on which extremely thin slices of tissues and organs have been placed. For protection, the sections are covered by a thin sheet of glass glued to the slide, called a coverslip.
Tissue or organ slices for observation under an optical microscope measure usually 5 to 10 µm in thickness, that is, 5 to 10 millionths of a meter.
Measurements used in Histology: 1 µm (1 micrometer) = 1 thousandth of a mm = 1 millionth of a meter.
Permanent histological slides are designed to last for many years. To obtain a permanent slide, fragments of tissues and organs or cells usually undergo a process called fixation. Fixation is carried out by chemical means (e.g. with formaldehyde) or physical means (e.g. by freezing).
Small fragments of tissues and organs are then subjected to several procedures, after which they can be cut in a device called microtome to obtain slices that can be observed under a light microscope. These slices are called histological sections.
Cells, as well as tissue and organ sections, are almost always colorless and need to be stained so that they can be observed under a light microscope. Finally, the sections are covered with a glass coverslip for protection.
Glass slides are also used to observe isolated cells, bacteria, protozoa and other microscopic objects.
Liver. Staining: hematoxylin and eosin (HE). Medium magnification.