Procedure for demonstrating lepra bacilli in paraffin sections.

The lesser degree of acid-fastness of lepra bacilli as compared with tubercle bacilli appears in a disagreeable manner in the difficulty of demonstrating the organisms of leprosy in paraffinized tissues (1). Faraco (2) showed that by ordinary methods of demonstrating acid-fast organisms the lepra bacilli are often not acid-fast, are not differentiated and may be stained by the counterstain. He devised a method of oiling the sections and staining with carbolfuchsin while the sections contained oil. Under these conditions the bacilli retained this dye. The method is effective but awkward and cumbersome. In working with similar procedures it has been found that staining before removal of the paraffin is satisfactory (though impracticable) and that replacement of the paraffin with a light oil produces still better results. The following procedure, which is not exactly a new method, has proved most valuable in demonstrating lepra bacilli in tissues, almost irrespective of the technics of fixation and embedding. It succeeds admirably with tissues indifferently fixed or embedded years previously where other procedures fail miserably. The use of picric acid in the fixative is contraindicated for this and other staining methods.