Figure 2. Giemsa staining was done to visualize the bacteria in tissues.

The bacteria were clearly visible within the tissues from the lungs, livers, kidneys, lymph nodes, brains, spleens, and blood from heart of the control animals that were only immunized with aluminum hydroxide adjuvant before they were infected with virulent Y. pestis strain 141. The lungs showed several large clumps of bacteria in the alveolar septum (a, arrows). Bacteria were also found inside blood vessels in the lungs (b, arrows) and blood from heart (d, arrows). Several large clumps of bacteria were shown in the hepatic sinus (c, arrows). Medullary cords of the lymph nodes were damaged and occupied by a large number of bacteria (e, arrows). The spleen show many large clumps of bacteria (f, arrows). Smaller clumps of bacteria are shown within the glomcrulus (g, arrows) and blood vessels in brain tissue (h, arrows).