Coloured scanning electron micrograph of a cluster of anthrax bacteria, Bacillus anthracis, in a capillary of the lung. Spongy tissue surrounding the capillary are lung alveoli. These rod-shaped, Gram positive bacteria are highly pathogenic; commonly an infection of livestock, B. anthracis is transmitted to humans by contact with contaminated animal hair, hides or excrement. Two forms of the disease occur: pneumonia in the lungs (woolsorters disease); severe ulceration of the skin (malignant pustules). Antibiotic treatment, if prompt, may be effective for skin infection. Pulmonary anthrax is fatal in most cases. Magnification: x810 at 6x4. 5cm size.