Light micrograph of acute pneumonia. Acute pneumonia is an infection of the lungs. Most commonly acute pneumonia is due to bacterial organisms, a colony of which can be seen in the centre of this image (collection of tiny blue dots). There are many neutrophils (larger blue dots) which are the inflammatory cells responding to the infection. The neutrophils occupy the space (white) in the lung alveoli. The alveolar spaces are bounded by thin septa (pink strands). Haematoxylin and eosin stained tissue section. Magnification: x400 when printed at 10cm.