[Solved]: Speed of fixation of tissues depends upon two…

Speed of fixation of tissues depends upon two factors; the rate of the individual fixative, and the of the tissue. For example, formalin penetrates the tissue at a rate of . Formalin and alcohol are known to penetrate the , and glutaraldehyde the worst. Mercurials and others are somewhere in between. Two factors that can speed-up the penetration process are; and . Heated formalin will fix tissues faster, and this is often the first step on an automated tissue processor. The of the fixative is also important, it should be a times the size of the tissue. The concentration of the fixative is best at its minimum level possible, for two reasons; one, it is cheaper and second; high concentration may damage the tissues. is best used fixative at a concentration of ; glutaraldehyde is generally made up at 0.25% to 4%. In order for a tissue to be microscopically, it must be placed on a glass — in extremely thin sections. This cannot be achieved without molding the tissue in such a form to make such sectioning possible. The tissue is and ——— with paraffin wax in order to be sectioned in sections ranging from 4-6 microns. The technique of getting fixed tissue into paraffin is called . The main steps in this process are; then before infiltration with wax. In tissue processing, the first step after fixation is . Fixed tissues, which is naturally aqueous, and cannot be directly infiltrated with paraffin as paraffin & water are and produce the undesirable crystals. Therefore, the water from the tissues must be by dehydration. This is usually done with a series of alcohol concentrations, say 70% to to 100%. The next step is called ” “, which is the controlled of the dehydrating chemical, and replacing it with a substance that is miscible with paraffin. The commonest clearing agent is . In the final step, the tissue is with paraffin. Various Paraffins with different melting point are available for purchase, for various hardnesses, depending upon the way the histo-technologist likes them and upon the climate of their use (warm vs. cold). A popular product called contains additive that make the paraffin blocks easier to cut. A , which applies negative pressure, is used inside the tissue processor to speed-up the of wax into the tissue.