156 BIOLOGY OF PNEUMOCOCCUS 



From the RI variant and from the R forms of Type II, were 

 derived the clear, mucinous colonies of Type III. The newly devel- 

 oped Type III strains were of relatively low virulence and fre- 

 quently remained localized at the site of subcutaneous inoculation. 

 A still wider shift which Griffith effected was that of a Group IVR 

 strain to virulent strains belonging to Types I and II. The injec- 

 tion of large doses of heated cultures of R pneumococci along with 

 small amounts of living R strains never caused a transformation of 

 type and only rarely produced a reversion of the R form of Type 

 II to its S form. Griffith, therefore, along with his success in chang- 

 ing R variants back to the original S forms with accession of viru- 

 lence and specific type characters, was the first to accomplish a 

 true transformation of one pneumococcal type into another. 



To degrade a pneumococcus in vitro to a form devoid of its 

 original type characters and then to exalt it to its original condi- 

 tion was an achievement that we had come to expect, but trans- 

 forming a degenerated or dissociated culture into another form 

 possessing entirely different type characters was a somewhat 

 amazing performance. Even remembering the theories of earlier in- 

 vestigators with their claims of species mutations, and discounting 

 possible errors in their experiments, this discovery had not been 

 anticipated. It was, for the first time, to supply a theoretical ex- 

 planation for the many baffling problems encountered in the study 

 of the spread and the invasiveness of pneumococci, and of the clini- 

 cal pathology of pneumococcal infections, not to mention the 

 broader bearing on the many riddles of microbiology. 



Neufeld and Levinthal 994 also were able to reproduce Griffith's 

 transformation phenomena, but by another procedure. They first 

 dissociated virulent, type-specific strains by growing the organ- 

 isms in broth containing sterile animal organs (spleen, heart, kid- 

 ney, and liver of rabbits). The degraded R variants were then 

 injected subcutaneously into mice with killed S pneumococci. Neu- 

 feld and Levinthal thus converted an avirulent Type IR pneumo- 

 coccus into a virulent Type IS organism, and with the addition of 



