Bacillus anthracis is a rod-shaped Gram-positive bacterium of size about 1 by 6 micrometres, and is the cause of the disease known as anthrax. B. anthracis was the first bacterium ever to be shown to cause disease, by Robert Koch in 1877. The specific name anthracis originates from the Greek word anthrax (ἄνθραξ), meaning coal, referring to the black skin lesions on the victims. The bacteria normally rest in spore form in the soil, and can survive for decades in this state. Once taken in by a herbivore, the bacteria start multiplying inside the animal and eventually kill it, then continue to reproduce in the carcass. Once they run out of nutrients there, they revert back to the dormant spore state.