Which of the following is not a cross-linking fixative?
(A) Osmium tetroxide (B) Glutaraldehyde (C) Methanol (D) Formaldehyde
(C) Chemical fixation This utilizes organic or non-organic solutions to maintain adequate morphological preservation. Chemical fixatives can be considered as members of three major categories: coagulant, cross-linking, and compound. Coagulant fixatives: Both organic and non-organic solutions may coagulate proteins making them insoluble. Cellular architecture in vivo is maintained primarily by lipoproteins and fibrous proteins such as collagen. Coagulating these proteins maintains tissue histomorphology at the light microscope level. Unfounately, because coagulant fixatives result in cytoplasmic flocculation and poor preservation of mitochondria and secretory granules, these fixatives are not useful in ultrastructural analysis. Examples: Ethanol, methanol, acetone, picric acid and trichloroacetic acid Cross-linking fixatives: Several chemicals were selected as fixatives secondary to their potential actions of forming cross-links both within and between proteins and nucleic acids. Examples include formaldehyde, glutaraldehyde and other aldehydes, e.g. chloral hydrate and glyoxal, as well as metal salts, e.g. mercuric and zinc chloride, and other metallic compounds, e.g. osmium tetroxide. useful for electron microscopic examination - Glutraldehyde (best one)/formaldehyde/osmium tetraoxide Compound fixatives: Alcoholic formalin