158 BIOLOGY OF PNEUMOCOCCUS 



tions. He found that type-specific S pneumococci could be trans- 

 formed from one specific S type into another specific S type 

 through the intermediate stage of the R form; that R forms of 

 pneumococci, derived from any specific S type, might be trans- 

 formed into S organisms of other specific types by injecting mice 

 subcutaneously with small amounts of living R strains together 

 with heated vaccines of heterologous S cultures. The S vaccines 

 could be heated for fifteen minutes between 60° and 80° and still 

 remain effective in causing R forms derived from heterologous S 

 types to revert to the type of the vaccine ; S vaccines heated fifteen 

 minutes at temperatures between 80° and 100° were not active in 

 causing R variants derived from heterologous S types to revert to 

 the type of the vaccine; S vaccines heated between 80° and 100° 

 could cause Type IIR and Type IIIR variants to revert to the 

 original S type ; S vaccines of any type, including Type I, heated 

 for fifteen minutes at 80° to 100° would no longer cause Type IR 

 strains to revert to their original S type; S vaccines heated for 

 periods as long as two hours at 60° were effective in causing R 

 forms derived from heterologous types to revert to the type of the 

 vaccine employed. Dawson successfully converted a single-cell R 

 strain derived from a Type HIS pneumococcus into a Type HIS, 

 a Type IS, and a Group IVS organism. On the other hand, every 

 attempt to produce transformation of type in vivo failed. 



TRANSFORMATION BY VACCINE AND ANIMAL INOCULATION 



In 1930, Dawson and Sia 305 announced the transformation of a 

 Type IIR into a Type HIS pneumococcus. The conditions neces- 

 sary for the reversal were minimal amounts of the R culture, the 

 addition of the heated activating culture, incubation for longer 

 than the conventional period, and the inclusion of small amounts 

 of anti-R serum and of blood broth. When the activating organ- 

 isms were heated for fifteen minutes at 100°, they lost their capac- 

 ity for inducing transformation, although suspensions heated for 

 four hours at 60° or for fifteen minutes at 80° were still effective. 



