The Effect of Preliminary Treatment (Fixing Fluids) on Staining Properties of the Tissues

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Abstract
As was reported in a previous paper,1 staining properties depend on the chemical composition of the tissues and on the strength of the dyes themselves. Applying mixtures of basic and acid dye on tissues (methylene blue, eosin Y) at different pH-values, it is possible to find differences in the isoelectric points of the nuclei and cytoplasm of different tissues. For example, the nucleus of polymorphonuclear cells of the blood consists of the most acid protein, with an isoelectric point around pH 2.5, while the nucleus of lymphatic tissues has an isoelectric point of about pH 4.0, and that of connective tissue about pH 3.4. With a knowledge of the above, a constant method of staining at various pH-values was used to study the effect of different fixing fluids on the staining properties of the tissues. In this way it was found that many fixing fluids gave very stable compounds with tissue proteins, and that they almost permanently change the chemical composition (i.e. the staining properties of the tissues). In some instances, these changes can be easily explained from the regular chemical standpoint. For example, formalin forms inert compounds with amino groups of the amino acids of proteins and in this way it makes the tissue proteins more acid, i.e. it moves the isoelectric point of the proteins toward a lower pH-value. The same is true in the case of the polivalent acids. The bivalent heavy metals such as mercury, on the contrary, it is assumed, combine with carboxyi groups of amino acids and in this way move the isoelectric point of the proteins toward a higher pH.

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