OVERVIEW OF METHODS USED IN HISTOLOGY / 1 TISSUE PREPARATION / 2 Hematoxylin and Eosin Staining With Formalin Fixation / 2 Other Fixatives / 2 Other Staining Procedures / 3 HISTOCHEMISTRY AND CYTOCHEMISTRY / 3 Chemical Composition of Histologic Samples / 3 Chemical Basis of Staining / 5 Enzyme Digestion / 7 Enzyme Histochemistry / 7 Immunocytochemistry / 7 Hybridization Techniques / 10 Autoradiography / 12 MICROSCOPY / 13 Light Microscopy / 13 Examination of a Histologic Slide Preparation in the Light Microscope / 14 Other Optical Systems / 15 Electron Microscopy / 18 Atomic Force Microscopy / 20 Folder 1.1 Clinical Correlation: Frozen Sections / 4 Folder 1.2 Functional Considerations: Feulgen Microspectrophotometry / 7 Folder 1.3 Clinical Correlation: Monoclonal Antibodies in Medicine / 9 Folder 1.4 Proper Use of the Light Microscope / 11
The objective of a histology course is to lead the student to understand the microanatomy of cells, tissues, and organs and to correlate structure with function.
The methods used by histologists are extremely diverse. Much of the histology course content can be framed in terms of light microscopy. Today, students in histology  laboratories use either light microscopes or, with increasing frequency, virtual microscopy, which represents a method of viewing a digitized microscopic specimen on a computer screen. In the past, more detailed interpretation of microanatomy was with the electron microscope (EM)—both the transmission electron microscope (TEM) and the scanning electron microscope (SEM). Now the atomic force microscope (AFM) can also provide high-resolution images, which are comparable in resolution to those obtained from TEM. Both EM and AFM, because of their greater resolution and useful magnification, are often the last step in data acquisition from many auxiliary techniques of cell and molecular biology.
These auxiliary techniques include:  histochemistry and cytochemistry,  immunocytochemistry and hybridization techniques,  autoradiography,  organ and tissue culture,  cell and organelle separation by differential centrifugation, and  specialized microscopic techniques and microscopes.
The student may feel removed from such techniques and experimental procedures because direct experience with them is usually not available in current curricula. Nevertheless, it is important to know something about specialized procedures and the data they yield. This chapter provides a survey of methods and offers an explanation of how the data provided by these methods can help the student acquire a better understanding of cells, tissues, and organ function.
One problem students in histology face is understanding the nature of the two-dimensional image of a histologic slide or an electron micrograph and how the image relates to the three-dimensional structure from which it came. To bridge this conceptual gap, we must first present a brief description of the methods by which slides and electron microscopic specimens are produced.
The routinely prepared hematoxylin and eosin–stained section is the specimen most commonly studied.
The slide set given each student to study with the light microscope consists mostly of formalin-fixed, paraffin-embedded, hematoxylin and eosin (H&E)–stained specimens. Nearly all of the light micrographs in the Atlas section of this book are of slides from actual student sets. Also, most photomicrographs used to illustrate tissues and organs in histology lectures and conferences are taken from such slides. Other staining techniques are sometimes used to demonstrate specific cell and tissue components; several of these methods are discussed below.
The first step in preparation of a tissue or organ sample is fixation to preserve structure.