. Cytological technique; the principles underlying routine methods. Histology -- Technique; Cytology -- Technique. INTRODUCTION TO FIXATION 19. NH2 HCR ^ )OH tyrosine c=o I OH General formula for HC(CH2)2C^ glutamic acid amino-acids \ \OH I Three amino-acids as part of a protein chain each amino-acid are written on the right of the formula in each case, although in fact they project in different directions; and the repeated part or backbone of the formula is shown as straight, though in nature it is folded, either to form a simple zigzag or in more complex ways. These conventions will be
. Cytological technique; the principles underlying routine methods. Histology -- Technique; Cytology -- Technique. INTRODUCTION TO FIXATION 19. NH2 HCR ^ )OH tyrosine c=o I OH General formula for HC(CH2)2C^ glutamic acid amino-acids \ \OH I Three amino-acids as part of a protein chain each amino-acid are written on the right of the formula in each case, although in fact they project in different directions; and the repeated part or backbone of the formula is shown as straight, though in nature it is folded, either to form a simple zigzag or in more complex ways. These conventions will be found to simplify the explanation of the reactions of proteins with fixatives and dves. The first requirement of a fixative is that it should not be proteolytic. Any substance that breaks the peptide links and sets free soluble amino-acids is the opposite of a fixative. The changes produced by a fixative must tend in the other direction, towards stability. One may broadly distinguish two kinds of fixation of protein, additive and non-additive. In the form_er, certain atoms of the fiixative combine chemically with some part of the protein and remain in combination. In the latter, no such obvious addition of atoms occurs. Ethanol is a non-additive fixative in the sense that none of its constituent atoms joins itself to protein, so far as is known. The 'nature' of the protein is, however, profoundly changed by its action, and the substance is therefore said to be. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Baker, John Randal, 1900-. London, Methuen; New York, Wiley
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