DODERLEIN BACILLI : These lactobacili appear as blue staining rods 1-2 μm in length in the background to the smear .They metabolise the glycogen in the intermediate cells and maintain the  acid pH of the vagina.They are particularly  abundant in smears from pregnant women .This results in cytolysis with destruction of the cytoplasm .The intermediate cells appear ragged and  bare intermediate cells nuclei are commonly seen. This pattern is sometimes seen in women on oral contraception and  in the late secretory  phase of the cycle.  Cytolysis can be so marked as to render a smear unsuitable for evaluation