2. Maceration Fluids. 33 per cent alcohol (24 hours); chromic acid 1:5000 (24 hours); potassium bichromate 0.1-0.2 per cent solution (2-4 days for nervous tissue); 0.1 per cent osmic acid (12-24 hours); 33 per cent potassium hydroxide (¼-1 hour, for muscle, tissue must be examined in the solution, as the cells dissolve when water is added); Arnold’s iodine solution (10 parts of a 10 per cent potassium iodide solution to which are added 5-10 drops of a solution containing 5 grms. of iodine and 10 grms. of potassium iodide in 100 cc. of water. Macerate one or more days. If solution becomes discolored add more of the second solution); very dilute formol solutions (1 cc. to 500 cc. physiologic salt-solution); Müller’s fluid (2-3 days, good for nervous tissue).
3. Glycerin. Used without diluting as a clearing agent, particularly when pigment is present; and as a mounting medium for stained preparations that cannot be put into alcohol.
4. Potassium Acetate. Saturated water solution for clearing and mounting fresh preparations. Does not clear as strongly as glycerin, hence is better adapted for the examination of fresh tissues.
5. Acetic Acid. 1-2-5 per cent solutions are usually employed. Clears the protoplasm and causes the nucleus to shrink slightly and to stand out more distinctly. It differentiates fatty and albuminous granules, dissolving the latter; and is useful in the demonstration of elastic tissue fibres, sharply outlining these against the connective-tissue which swells and becomes clear.
6. Acetic Acid Fuchsin. A few drops of fuchsin are added to a 2 per cent solution of acetic acid. With this solution the nuclei are not only brought out more sharply but they are stained red.
7. Lugol’s Solution. Dilute Lugol’s solution to a pale yellow color. It brings out the contours of cell and nucleus, and has a specific reaction with glycogen and amyloid, giving both a brown color. Since glycogen is dissolved out in water-solutions tests for glycogen in fresh tissues should be made with iodine-glycerin or iodine-gum (Lugol’s one part, gum arabic 100 parts). Smears or cover-glass preparations may be placed in covered dishes containing a few crystals of iodine.
8. Potassium and Sodium Hydroxides. In solutions of 1-3 per cent all tissue-structures swell and dissolve or become unrecognizable except elastic fibres, fat, pigment, amyloid, bacteria, yeasts and moulds. Used especially for examination of skin-scrapings or pus for presence of blastomyces and various forms of parasitic moulds (barber’s itch, ringworm, tinea, etc.). Solutions of 33 per cent clear the tissues but do not destroy the cells. Useful for maceration. When diluted the cells are destroyed.
9. Mineral Acids. HCl or H2SO4 (3-5 per cent). Used to dissolve areas of calcification. Calcium dissolves with liberation of CO2; the phosphates dissolve without gas-formation, but with H2SO4 form crystals of calcium sulphate. Sulphuric acid is also used as a test for cholesterin (red or violet coloration), and with iodine as a test for amyloid.
10. Osmic Acid. In a 1 per cent solution this is used to test for the presence of fat (oleates), the fat-droplets become black or brown.
11. Sudan III or Scharlach R. Alcoholic solutions of these dyes are used for the demonstration of fat in fresh tissues. They stain fat orange to scarlet. (For method see Staining of Fat.)