Staining Method of Preston and Morrell
The method given by Preston and Morrell (4) is recommended because it gives reliable result and does not require standardization of decolourizing period. Take a fixed smear and cover it with ammonium oxalate crystal violet solution (S23) and allow to react for 30 seconds. Pour off the stain and wash the smear with undiluted Grams iodine (S24). Flood the smear with fresh iodine for 30 seconds.
Pour off iodine solution and wash the smear with iodine-acetone mixture (S26). Cover the smear with the same solution (S26) and allow it to react for 30 seconds. Wash with water and counterstain with 10 times diluted carbol fuchsin (S19) for 30-40 seconds. Wash, dry and examine under oil immersion objective.
