The slides are cleaned with pumice in the usual way. An agar slope culture of the organism to be stained from six to twenty-four hours old is selected. A bit of the culture is removed and placed in a watch-glass of water. The bacteria are allowed to diffuse of themselves without stirring. After several minutes a loop of this water is removed and three streaks are made across the slide, one in the middle and one on each side of this about one-quarter of an inch from it. This gives well scattered bacteria in one of the three streaks at least and very little other material on the slide to cause precipitates. The slide is carefully dried and fixed and then covered with an abundance of the mordant by filtering through a small filter onto the slide so that the mordant shows transparent on the slide. The preparation is then gently warmed and cooled three times, adding mordant if necessary. _Do not heat to steaming._ After mordanting for about five minutes the excess is washed off under the tap. It is a good plan to hold the slide level and allow the water to run into the center of the mordant and flow it off. Inclining the slide is apt to cause the film on the surface of the mordant to settle down on the slide and spoil the preparation. After the mordant is washed off and all traces of it removed with a clean cloth if necessary the stain is applied and gently heated and cooled the same way for from three to five minutes. The preparation is then washed, dried and examined. The mordant used is a modification of Löffler’s which is somewhat simpler in preparation since the stock solution of FeCl₃ is more permanent than FeSO₄ solution. Mordant sufficient for one student: 5 per cent. solution of FeCl₃ 20.0 cc 25 per cent. solution of tannic acid 20.0 cc Anilin fuchsin 4.0 cc Normal NaOH 1.5 cc The solution of FeCl₃ is made up in the cold and must be perfectly clear. The tannic acid solution must be thoroughly boiled and filtered until clear. The iron and the acid are carefully mixed, boiled and filtered clear. The anilin fuchsin must be added slowly with constant stirring and the mixture boiled and filtered. The NaOH is added in the same way and this mixture boiled and filtered. The final mordant should not leave a film on a clean slide when poured on and allowed to run off. Unless the mordant is in this condition and perfectly clear, it should not be used, but a new one must be made up. Time and care in the preparation of the mordant are essential. The stain to follow this mordant is anilin fuchsin. =Staining of Metachromatic Granules.=--_Neisser’s Method._ Prepare the film in the usual way. Stain with Neisser’s stain a few seconds only. Wash and stain with Bismarck brown a few seconds only. _Neisser’s Stain_: