a carbuncle.-a malignant pustule.-a microscopic, bacterial organism (bacillus anthracis), resembling transparent rods. [see illust. under bacillus.]-an infectious disease of cattle and sheep. it is ascribed to the presence of a rod-shaped bacterium (bacillus anthracis), the spores of which constitute the contagious matter. it may be transmitted to man by inoculation. the spleen becomes greatly enlarged and filled with bacteria. called also splenic fever.