54 PART III Sample Preparation in Light Microscopy
Squash Slides
A simple way to prepare a thin sample is to squash or flatten a small piece of tissue
under the coverslip. Designed for soft samples, squash slides begin by preparing
a wet mount; place the lens tissue over the cover glass; gently press down,
careful not to destroy the sample or break the cover glass, and squash the sam-
ple, then remove excess water.
Stained Tissue Section
A more complicated sectioning procedure occurs when the structure and organization
of a whole small organism or a tissue piece needs study. For most samples,
first the tissue is preserved and hardened and the water is removed. Then the
sample is embedded in a rigid medium such as wax or plastic and sliced into
very thin sections only several microns thick using a precision machine called
a microtome. The sample is oriented to give cross-sections or longitudinal sections
when sliced. The sections are adhered onto microscope slides, the embedding
medium removed – except when you use plastic – and the tissues stained to
differentiate structures and cells. If fast working is essential, as is often the case in
surgical biopsies for cancer, the samples are frozen, sliced with a freezing microtome,
stained and examined.
Pre-Prepared Slides
Especially useful for educational purposes and for those who do not want to
undertake the laborious process of creating their own slides, prepared micro-
scope slides are available in all areas of science, including plants, animals, single
cell organisms, organ or tissue cells, blood, bacteria and so on. Prepared micro-
scope slides also offer access to infectious bacteria, animal tissue, marine life, diseased
cells and other specimens that may not be easily available to students or hob-
byists. In addition, they can be used as controls for students and researchers to
compare their own samples.