CHAPTER 11 - FIXATION

Abstract

This chapter discusses chemical fixatives and fixations in detail. Fixation is the basis of histological technique, and the results of all subsequent procedures depend on the selection and correct use of fixatives. It is essential to understand the action of these substances upon the cell and tissue constituents. Fixatives serve three main functions: (1) they cause sudden death of the cell, (2) they coagulate and preserve the various proteins, carbohydrates, and lipoids, of which the cell is composed, and (3) they render the cell resistant to shrinkage during subsequent processing. The chapter also highlights the concept of simple fixatives and compound fixatives. Many fixatives have been devised, but only about 10 formulae are used in routine work. The chapter describes the action of the simple fixatives upon the cell and tissue constituents. Formaldehyde, mercuric chloride, osmium tetroxide, picric acid, acetic acid, ethyl alcohol, potassium dichromate, and chromic acid are some of the simple fixatives. Compound fixatives may be conveniently considered under two headings: (1) Microanatomical and (2) cytological. Microanatomical fixatives are used for preserving the various layers of tissue and cells in relation to one another, so that general structure may be studied. Cytological fixatives are usually subdivided into two groups: (1) nuclear and (2) cytoplasmic.