Fixation may also be effected by immersing in some fixative fluid, such as one of the following: 1. Absolute alcohol, for five to fifteen minutes. { equal parts, for five to thirty 2. Absolute alcohol, { minutes (e. g., for blood or Ether, { milk). 3. Osmic acid, 1 per cent. aqueous solution, for thirty seconds. 4. Corrosive sublimate, saturated aqueous solution, for five minutes. 5. Corrosive sublimate (Lang), for five minutes. This solution is prepared by dissolving: Sodium chloride 0.75 gramme Hydrarg. perchloride 12.00 grammes Acetic acid 5.00 grammes In distilled water 100.00 c.c. Filter. 6. Gulland's solution, for five minutes. This solution is prepared by mixing: Absolute alcohol 25.0 c.c. Ether 25.0 c.c. Corrosive sublimate, 20 per cent. alcoholic solution 0.4 c.c. 7. Formalin 10 per cent. aqueous solution (= 4 per cent. aqueous solution of formaldehyde since formalin is a 40 per cent. solution of the gas in water). Either of these methods of fixation coagulates the albuminous material and ensures perfect adhesion of the film to the cover-slip. _Clearing._--Wash the cover-slip thoroughly in running water and proceed with the staining. If the film has been prepared from broth, liquefied gelatine, or pus or other morbid exudations, saturate the film after fixation with acetic acid 2 per cent. and allow it to act for two minutes. Wash with alcohol, then let the alcohol remain on the cover-slip for two minutes. (This will "clear" the groundwork and give a much sharper and cleaner film than would otherwise be obtained.) If the film has been prepared from blood or bloodstained fluid, treat with acetic acid 2 per cent. for two minutes after fixation. Wash with water, dry, and proceed with the staining. (This will remove the hæmoglobin and facilitate examination.) _Staining._-- 1. Rest the cover-slip, film side uppermost, on the rubber mat. 2. By means of a drop-bottle, cover the film side of the cover-slip with the selected stain, allow it to act for a few minutes, then wash off the excess in running water. The penetrating power of stains is increased by (a) physical means--e. g., heating the stain; (b) chemical means--e. g., by the addition of carbolic acid, 5 per cent. aqueous solution; caustic alkalies, 2 per cent. aqueous solutions; water saturated with aniline oil; borax, 0.5 per cent. aqueous solution. The most commonly used dyes for cover-slip film preparations are the aniline dyes. (A) Basic: (a) Methylene-blue. (b) Gentian violet. (c) Fuchsin. These dyes are kept in saturated alcoholic (90 per cent.) solutions so that decomposition may be retarded.