The discovery of pneumococcal type transformation: an appreciation

Abstract

The remarkable paper by Fred. Griffith on the significance of pneumococcal types, reproduced in the preceding pages of this Journal, in which it was first published 38 years ago (Griffith, 1928), describes a series of careful and painstaking experiments which show beyond doubt that the ability to produce a polysaccharide capsule can regularly be restored to ‘rough’ (R) strains of pneumococci which have lost it, by the subcutaneous inoculation of mice with a mixture of a small number of the living R bacteria and an excess of heat-killed, capsulated (S) virulent bacteria. The inoculated mice frequently died from septicaemia and virulent, capsulated S organisms could be isolated from the blood. On the other hand, in control experiments, the injection of suspensions of heat-killed S bacteria alone never yielded living organisms, while recovery of virulent S organisms by (mutational) reversion, following inoculation of living R bacteria alone, was a rare event. Griffith called this phenomenon ‘transformation’ and, at least in the field of bacterial genetics, this name is still specifically used to describe it.