A new metachromatic stain technique for paraffin-embedded neural tissue using thionin.

A metachromatic staining procedure which differentiates Nissl substance in neuron cell bodies, neuropil area, and axonic fibres of passage with distinct colours with no counterstaining has been developed for paraffin-embedded tissue utilizing thionin stain. Frozen sections of neural tissue fixed in formalin may also be satisfactorily stained by this procedure, and both paraffin-embedded and frozen sections have been found to retain the distinct colours for a year with little fading. Since metachromatic staining of paraffin-embedded neural tissue has not been successfully achieved before, the following procedure will be especially valuable for studying small vertebrate brains, or other central nervous tissue which must be processed by the paraffin method.