The image is showing MC Faydens reaction.
Bacillus anthracis, the organism that causes anthrax,a large Gram positive, aerobic, rod shaped,spore bearing bacillus, is the only obligate pathogen within the genus bacillus.
When a blood film containing anthrax bacilli is stained using polychrome methylene blue for a few seconds and observed under microscope, a purplish coat of amorphous material is seen around a blue stained bacilli. The amorphous purple material is the capsule. This is called Mc Fadyean’s reaction and is used in the presumptive diagnosis of anthrax