Abstract
A bacteriophage is described which attacks almost exclusively strains of Bacillus anthracis, and attacks all the strains of this species which have been tested.As well as attacking typical strains of this species it attacks atypical variants.Strains of B. anthracis are not attacked by this phage when they are in a muciod state.A few strains of B. anthracis are only feebly attacked by this phage. Some experiments, conducted in an attempt to discover the reason for this, are described.The results are discussed and arguments in favour of regarding B. anthracis as a valid species are put forward.