Causative organism of anthrax, an acute septicaemic infection of sheep and other animals, transmissable to man. Non-motile, capsulated, straight aerobic spore bearing bacterium 4-8×1- IViiim in size. Gram-positive and peculiarly rectangular in shape. Blood films from infected animals, stained with polychrome methylene blue, show teeming masses of the bacilli, and between them purplish amorphous material derived from degenerate capsules of effete organisms (McFadycan’s reaction). Old infected material may be confirmed as anthrax-infected by precipitin reaction between prepared antiserum and tissue extract (Ascoli’s reaction).