chemical examination of stool ( feces), occult Blood or pH

Principle: –

Peroxidase type action of hemoglobin in the blood (present in the specimen) converts hydrogen peroxide to water and nascent oxygen. This oxygen oxidizes benzidine (in acidic medium) to form green to blue colored complex.

Requirement:-

1 Glass slides

2 Applicator stick or wire loop

3 Glacial acetic acid

4 Hydrogen peroxide (30% v/v)

5 Benzidine powder

Specimen:-

Feces

1. Take pinch of benzidine powder in a small test tube.

2. Acidify it with 2 to 3 drops of glacial acetic acid and mix well.

3. Add about 1.0 ml of hydrogen peroxide and mix well.

4. Place small quantity of stool specimen on a clean and dry glass slide.

5. Place one or two drops of the benzidine-glacial acetic acid-hydrogen peroxide mixture on the stool specimen on the glass slide.

6.Observe change in color.

Observation:-

1. No change in color: Occult blood absent

2. Color changes to green to blue: Occult blood present.