138 TRANSFORMATION OF PNEUMOCOCCAL TYPES 



specific transformation in vitro using sterile extracts of S cells from which all formed 

 elements and cellular debris had been removed by Berkefeld filtration. He thus 

 showed that crude extracts containing active transforming material in soluble form 

 are as effective in inducing specific transformation as are the intact cells from which 

 the extracts were prepared. 



Another example of transformation which is analogous to the interconvertibility of 

 pneumococcal types lies in the field of viruses. Berry and Dedrick (7) succeeded in 

 changing the virus of rabbit fibroma (Shope) into that of infectious myxoma (San- 

 arelli). These investigators inoculated rabbits with a mixture of active fibroma virus 

 together with a suspension of heat-inactivated myxoma virus and produced in the 

 animals the symptoms and pathological lesions characteristic of infectious myxoma- 

 tosis. On subsequent animal passage the transformed virus was transmissible and 

 induced myxomatous infection typical of the naturally occurring disease. Later 

 Berry (8) was successful in inducing the same transformation using a heat-inacti- 

 vated suspension of washed elementary bodies of myxoma virus. In the case of these 

 viruses the methods employed were similar in principle to those used by Griffith in 

 the transformation of pneumococcal types. These observations have subsequently 

 been confirmed by other investigators (9). 



The present paper is concerned with a more detailed analysis of the phenome- 

 non of transformation of specific types of Pneumococcus. The major interest 

 has centered in attempts to isolate the active principle from crude bacterial 

 extracts and to identify if possible its chemical nature or at least to charac- 

 terize it sufficiently to place it in a general group of known chemical substances. 

 For purposes of study, the typical example of transformation chosen as a 

 working model was the one with which we have had most experience and which 

 consequently seemed best suited for analysis. This particular example repre- 

 sents the transformation of a non-encapsulated R variant of Pneumococcus 

 Type II to Pneumococcus Type III. 



EXPERIMENTAL 



Transformation of pneumococcal types in vitro requires that certain cultural 

 conditions be fulfilled before it is possible to demonstrate the reaction even in 

 the presence of a potent extract. Not only must the broth medium be optimal 

 for growth but it must be supplemented by the addition of serum or serous 

 fluid known to possess certain special properties. Moreover, the R variant, 

 as will be shown later, must be in the reactive phase in which it has the capacity 

 to respond to the transforming stimulus. For purposes of convenience these 

 several components as combined in the transforming test will be referred to 

 as the reaction system. Each constituent of this system presented problems 

 which required clarification before it was possible to obtain consistent and 

 reproducible results. The various components of the system will be described 

 in the following order: (1) nutrient broth, (2) serum or serous fluid, (3) strain 

 of R Pneumococcus, and (4) extraction, purification, and chemical nature of 

 the transforming principle. 



