DISSOCIATION AND TRANSFORMATION 159 



Filtrates of vigorously growing cultures and of heat-killed suspen- 

 sions of S organisms were inactive, as also were suspensions of S 

 organisms disrupted by freezing and thawing, with subsequent 

 heating for fifteen minutes at 60°. But when suspensions of S or- 

 ganisms were first killed by heating for fifteen minutes at 60° and 

 then frozen and thawed, they were highly effective. In a more de- 

 tailed communication, the authors gave the additional information 

 that transformation of type could be induced by the use of small 

 amounts of S vaccine, and that while the transformative process 

 was brought about most readily by employing anti-R serum in the 

 culture medium, it might be accomplished without the presence of 

 the serum. 



Transformation of one S form to the S form of a different type 

 without any apparent development of intermediate stages was de- 

 scribed by Dawson and Warbasse 306 in 1931. The original culture 

 was a virulent, single-cell isolation of Type II Pneumococcus. One 

 drop of a 10" 6 dilution of the culture was seeded into a medium 

 containing homologous immune serum together with large quanti- 

 ties of Type III pneumococcal vaccine. The cultures were incu- 

 bated at 37°, and at the end of forty-eight hours streaked plates 

 showed, in the majority of instances, numerous Type III with 

 some Type IIS colonies. No R colonies were observed. From the 

 experiment Dawson and Warbasse inferred that a type-specific S 

 pneumococcus can be transformed into other type-specific S pneu- 

 mococci by growth in homologous immune serum in the presence of 

 heterologous vaccine. Although the conditions of the experiment 

 were unfavorable to the development of R forms, the authors 

 thought it was probable that the organism nevertheless passed 

 through this intermediate stage during the transformation. 



In 1931, Sia and Dawson 1272 reported that R cultures possess- 

 ing slight degrees of R stability were most suitable for transforma- 

 tion experiments in vitro. The authors also sought a soluble prin- 

 ciple in cultures subjected to the action of bacterial enzymes 

 liberated in old broth cultures and during mechanical disruption of 



