. Manual of bacteriology. Bacteriology. 98 MICROSCOPIC METHODS. than that of methylene-blue and it approaches the violets in tint. Bismarck-brown is a weak stain, but is useful for some purposes. Formerly it was much used in photomicrographic work, as it was less actinic than the other stains. It is not, however, needed now, on account of the improved sensitiveness of plates. It is most convenient to keep saturated alcoholic solutions of the stains made up, and for use to filter a little into about ten times its bulk of distilled water in a watch-glass. A solution, of good body is thus obtaine
. Manual of bacteriology. Bacteriology. 98 MICROSCOPIC METHODS. than that of methylene-blue and it approaches the violets in tint. Bismarck-brown is a weak stain, but is useful for some purposes. Formerly it was much used in photomicrographic work, as it was less actinic than the other stains. It is not, however, needed now, on account of the improved sensitiveness of plates. It is most convenient to keep saturated alcoholic solutions of the stains made up, and for use to filter a little into about ten times its bulk of distilled water in a watch-glass. A solution, of good body is thus obtained. Most bacteria (except those of tubercle, leprosy, and a few others) will stain in a short time in such a fluid. Watery solutions may also be made up, a saturated watery solution of methylene-blue or a i per cent solution of gentian-violet. Stains must always be filtered before use; otherwise there may be deposited on the preparation granules which it is impossible to wash off. The violet stains in solution in water have a great tendency to decompose. Only small quantities should therefore be prepared at a time. The Staining of Cover-glass Films. — Films are made from cultures as deseribed above. The cover-glass may be floated on the surface of the stain in a watch-glass, or the cover-glass, held in forceps with the film side uppermost, may have as much stain poured on it as it will hold. When the preparation has been exposed for the requisite time, usually a few minutes, it is well washed in tap water in a bowl, or with distilled water with such a simple contriv- ance as that figured (Fig. 52). The figure explains itself. When the film has been washed, the surplus of water is drawn off with a piece of filter paper, the preparation is carefully dried high over a flame, a drop of xylol-balsam is applied, and the cover- glass mounted on a slide. It i^ sometimes advantageous to examine films in a drop of water in place of balsam. The films can be subsequently dried and mo
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