Abstract
The ordinary dyes, when applied to bacteria, do not stain well the mycelium and the spores of the fungi. Slightly better results are obtained if the dyes are steamed. Some procedures apply Gram's iodine, after the respective dye was used. Similarly, the use of spore staining methods is less satisfactory as compared with those observed in staining bacterial spores. In order to obtain more effective staining, the influence of mordants was tested. Smears of fungi were steamed with a mordant preceding the staining. This mordant consists of 2 solutions: Solution A., contains 100 gm. of tannic acid dissolved in 100 cc. of 95% alcohol, and solution B., which consists of 92.5 cc. of 50% formalin, and 7.5 cc. of glacial acetic acid. Before use, one part of solution A and 2 parts of solution B are mixed uniformly; this mixture represents the mordant to be used. Separately, either solution keeps indefinitely. The fixed smear is covered with the mordant-mixture, steamed for 5 minutes, and washed off the slide with warm water. The slide is covered with the respective stain, steamed for 3 to 5 minutes, and washed.
Used after the mordant, almost any of the ordinary dyes give satisfactory results. Particularly good results were obtained with Loeffler's methylene blue, gentian-violet, brilliant green, fuchsin, and safranin. In instances where darker staining is required (for photographic purposes), the application of the stain is followed by steaming with Gram's iodine for 3 to 5 minutes, thus rendering the fungi and their spores almost black (if methylene blue or gentian violet is used).
The application of the mordant also greatly improves the contrasting spore staining methods of bacteria when applied to fungi.
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