Slide 2. Normal salivary flora
Photographed through an oil-immersion lens, this unacceptable specimen contains epithelial cells and a few neutrophils. These two kinds of cells can be differentiated by their size and the structure of their nuclei. The slide shows the wide variety of bacteria normally present in saliva: gram-positive cocci singly and in pairs, chains, and clusters; gram-positive bacilli (probably “diphtheroids”); and gram-negative bacilli of varying sizes and shapes (possibly oral anaerobes).

Slide 3. Epithelial cells
Gram-positive diplococci adhere to two large epithelial cells with abundant cytoplasm. A few such epithelial cells do not invalidate satisfactory sputum specimens. However, in determining the cause of pneumonia, the examiner should disregard bacteria adherent to epithelial cells. The bacteria are oral flora, not pathogens expectorated from the lungs, where no squamous epithelial cells exist.

Slide 4. Artifact Precipitated
crystal violet stain may resemble cocci. The clues are the dense clumping, the small size of the gram-positive dots, and the paucity of organisms elsewhere in the field.

Slide 5. Artifact
Precipitated crystal violet can produce masses of needle-like material that can resemble gram-positive bacilli. The dense clumping of the stain is characteristic.

Slide 6. Underdecolorized stain
The multilobed nuclei of the neutrophils are stained purple rather than red. This indicates that decolorization and counterstaining should be repeated.