Abstract
In 1921 Arkwright described two distinct types of colonies which appeared when cultures of Bacillus dysenteriae Shiga were plated on agar. One which he called the “rough” type had a coarsely granular surface rather like morocco leather, and an irregular margin. The other which he called the “smooth” type had a regular edge and a smooth surface. He found the same differentiation into rough and smooth colonies occurred among other member of the group, in B. typhosus, in B. paratyphosus B, and in B. enteritidis Gaertner. Since then these two types of colonies have been described in many other organisms; in streptococci by Cowan, in pneumococci by Griffith and by Reimann, in pasteurella by de Kruif, in meningococcu and gonococcus by Atkin, in the cholera vibrio by Shousha.
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