Light micrograph of a cervical smear containing normal squamous cells and numerous tiny rod-shaped Lactobacillus bacteria. These bacteria are a normal part of the flora in the vagina of the sexually mature human female. Lactobacillus ferments lactic acid from the glycogen in the epithelial lining of the vagina. The acidic environment that they produce inhibits the growth of many other bacteria and so protects the vagina from infection. Cervical smear tests are routinely performed to check for abnormalities in cells of the cervix, which might indicate the onset of cancer.