you are making the smear, prevent blood from reaching the extreme edges of the slides. Allowing the smear to reach the edges of the slide will aggravate the tendency of large cells to stack up on the perimeter of the smear. A smear with wavy lines or blanks spots should be discarded, and a new smear made. 5. Once the blood smear is made, let it dry (it will take a few minutes). Then write the patient’s name in pencil on the bottom edge of the slide, as illustrated in figure 7-18, view D). Proceed to step 2, staining the cells. STAINING THE CELLS.—Once a blood smear is made, it should be stained. Staining the blood smear highlights the differences among the different types of leukocytes for easier recognition during the counting process. The most popular stain used for this purpose is Wright’s stain. Wright’s stain is a methyl alcohol (methanol) solution of an acid dye and a basic dye. The acid dye in Wright’s stain is known as eosin and is red in color. The basic dye in Wright’s stain is known as methylene blue and is blue in color. Generally, white cells are identified by their affinity to the dye they prefer. For example, cells that prefer the acid dye (eosin) are called eosinophils. Other cells that prefer the basic dye are called basophils. WARNING Wright’s staining solution contains methanol, which is considered a hazardous material. It is classified as flammable, a poison, and an irritant. Methanol must be kept away from heat, sparks, and open flames. Good ventilation in usage areas is paramount since exposure to vapors can irritate eyes, nose, throat, and mucous membranes of the upper respiratory tract. When not in use, methanol containers should be closed tightly and stored upright to prevent leakage. Gloves and protective clothing (e.g., lab coat or apron) and eyewear should be worn to avoid contact with the solution. Absorption through skin can cause permanent blindness. Death may result from ingestion or exposure to high vapor concentrations of methanol. There are a variety of staining products on the market today. Some of these staining products have combined Wright’s solution with other staining solutions, such as Giemsa stain. When using a new product, you should always review the manufacturer’s usage and safety recommendations. The staining process that we will cover in this chapter is known as a quick stain. A quick stain has very few equipment requirements and only a few procedural steps. An example of a quick stain is One Step II Wright-Giemsa Stain Solution® by Criterion Sciences. To stain a blood smear with this product, follow the steps below. 1. Prepare two staining containers by filling one with One Step II stain solution and the other with deionized or distilled water. The use of tap water instead of deionized or distilled water is not recommended since the pH of tap water varies. If tap water is used, its pH should between 5.8 and 7.03. 2. Immerse the slide (blood smear) in the stain for 15 to 30 seconds. (To prevent debris or precipitate from contaminating the slide, do not add new stain to old.) 3. Remove the slide and allow excess stain to drain from the edge of the slide. 4. Immerse the slide in the deionized or distilled water for 5 to 15 seconds. (Change the water 7-22 A B C D HM3f0718 Figure 7-18.—Making a blood smear: A. Placing second slide at a 23Eangle; B. Blood distributing itself along second slide’s edge; C. Drawing blood across surface of slide; D. Example of a properly prepared blood smear.