Читать книгу Practical Guide to Diagnostic Parasitology - Lynne Shore Garcia - Страница 84

PVA is a plastic resin that can be incorporated into Schaudinn’s fixative (or other liquid fixatives). The PVA powder is not a fixative but serves as an adhesive for the stool material; i.e., when the stool-PVA mixture is spread onto the glass slide, it adheres because of the PVA component. Fixation is still accomplished by the Schaudinn’s fluid itself. Perhaps the greatest advantage in the use of PVA is the fact that a permanent stained smear can be prepared. PVA fixative solution is highly recommended as a means of preserving cysts and trophozoites for later examination. The use of PVA also permits specimens to be shipped (by regular mail service) from any location in the world to a laboratory for subsequent examination. PVA is particularly useful for liquid specimens and should be used in the ratio of 3 parts PVA to 1 part fecal specimen. The formula is as follows:

PVA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 g

Ethyl alcohol, 95% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.5 ml

Mercuric chloride, saturated aqueous . . . . . . . . . . . . . . . . . 125.0 ml

Acetic acid, glacial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 ml

Glycerin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ml

Mix the liquid ingredients in a 500-ml beaker. Add the PVA powder (stirring is not recommended). Cover the beaker with a large petri dish, heavy wax paper, or foil, and allow the PVA to soak overnight. Heat the solution slowly to 75°C. When this temperature is reached, remove the beaker and swirl the mixture for 30 s until a homogeneous, slightly milky solution is obtained.

Summary: PVA