A Comparative Study of Smooth and Rough Pneumococcus Colonies

Our knowledge of the production of variant pneumococcus forms has been greatly clarified during the last few years by recognition of the fact that the species may be divided into at least two great groups including the so called S, or smooth forms, and the R, or rough forms. Although the terms rough and smooth have been derived essentially from the morphological characteristics of the colonies formed by respective organisms of each group, they also bear a significant relationship to virulence, serological, and other properties exhibited by the organism. This general concept of bacterial dissociation into rough, smooth, and possibly other groups has not only facilitated the classification of pneumococcus variants but also those of other forms. I t has found application in a great variety of bacterial species and, as has recently been emphasized by Hadley's review (1), has become of fundamental importance in bacteriology. With the pneumococcus a number of features have been recognized as characteristic of the R strains, serving to differentiate them from the S or parent strains. Primarily the surface colonies formed by R strains are atypical, presenting a rough surface in contrast to the typical smooth surfaced colonies of the S forms (2-6). Other recognized properties of the R pneumococcus include those of avirulency for mice,* loss of capsule, inability to produce the so called pneumo-