CONTROL BY FACTORS DISTINCT FROM THE S TRANSFORMING P R I N C I P L E OF THE AMOUNT OF CAPSULAR POLYSACCHARIDE PRODUCED BY TYPE I I I PNEUMOCOCCI BY COLIN M. MAcLEOD, M.D., Al~O

Mutants of several pneumococcal types have been described which form smaller amounts of capsular polysaccharides than the parent or normally encapsulated strain from which they derived. S transforming principles from these mutants confer on certain R strains of pneumococcus the capacity to produce amounts of polysaccharide characteristic of the S mutants. I t has been suggested that the transforming principles of strains showing differences in polysaccharide synthesis bear a relation to each other similar to that of the genes of an allelic series (1-3). In discussing the mechanisms involved in differences in polysaccharide formation it was suggested earlier (1) that variation might depend not only on "atlelic" differences in the S transforming principles but also on some other system in the cell capable of modifying polysaccharide production. The present paper is concerned with the demonstration that polysaccharide formation can be modified by factors distinct from the S transforming principle. I t has been shown that encapsulated pneumococci may possess and reduplicate normal S transforming principle and yet produce much less polysaccharide than would be expected if the nature of the S transforming principle were the sole determinant.