An AIDS patient develops symptoms of pneumonia, and Pneumocystis carinii is suspected as the causative organism. Bronchial lavage is performed. Which of the following stains would be most helpful in demonstrating the organism's cysts on slides made from the lavage fluid?

The appropriate stain is methenamine silver, and the requisition slip when submitting the wash fluid should have a reference to either Pneumocystis or methenamine silver, since routine hematoxylin and eosin does not adequately demonstrate the organisms. The cysts, when stained with methenamine silver, have a characteristic cup or boat shape; the trophozoites are difficult to demonstrate without electron microscopy. It is also woh knowing that sputum samples are not nearly as effective as bronchial washes in demonstrating the organisms.Alcian blue is good for demonstrating mucopolysaccharides.Hematoxylin and eosin is the routine tissue stain used in pathology laboratories. Prussian blue is good for demonstrating iron.