Collection of stool samples Three stool samples for parasitological examination will be taken from both control subjects and CRC patients at 1-2 days interval. Stool samples were collected in individual containers, containing 5 ml of Turdiev's preservative provided conservation and staining of protozoa cysts and eggs of worms for a year. The Turdiev's preservative includes:80 ml of 0.2% aqueous solution of sodium nitrite, 10 ml of formaldehyde, 2 ml of glycerin, 8 ml of Lugol's solution, 250 ml of distilled water.