STAINING PROPERTIES OF BRAIN TISSUE BEFORE AND AFTER TREATMENT WITH POTASSIUM DICHROMATE

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Abstract
This paper deals with the influence of the pH and of salts on the staining of brain tissue with basic and acid stains, before and after treatment with potassium dichromate. The pH value and the ratio UO2++/Ba++ for destaining identify the ionized groups of tissue. In frozen sections of the brain the metachromatic staining of myelin sheaths results from interaction of phosphate containing compounds with toluidin blue. In the nerve cells also, phosphate groups in the Nissl substance and the nucleus form the substrate of staining, though it is probable that carboxyl groups are also involved in the process. In paraffin sections, after treatment with alcohol, the phosphate-containing substances of the myelin sheaths are dissolved and a residual protein skeleton remains, which contains carboxyl groups. Frozen sections stained with acid stains at a pH lower than 4.5 present an over-all staining of all elements except for the myelin sheaths which remain "empty". In paraffin sections the residual protein skeleton is also stained by acid stains. Brain tissue fixed in dichromate before contact with alcohol shows a staining picture with acid stains identical with that of frozen sections, which means a selective staining of axons, cells and gray substance. The precipitated myelin seems to enclose the protein skeleton and to prevent an acid stain from gaining the positive groups. While myelin regularly shows phosphate groups, precipitated myelin contains carboxyl groups. The results of the findings are discussed as to their significance in general and also in relation to Alzheimer-Mann-Häggqvist's method for staining brain tissue.