140 TRANSFORMATION OF PNEUMOCOCCAL TYPES 



consequent loss of both type specificity and the capacity to produce infection 

 in the animal body. The designation of these variants as R forms has been 

 used to refer merely to the fact that on artificial media the colony surface is 

 "rough" in contrast to the smooth, glistening surface of colonies of encapsulated 

 S cells. 



The R strain referred to above as R36A was derived by growing the parent S 

 culture of Pneumococcus Type II in broth containing Type II antipneumococcus 

 rabbit serum for 36 serial passages and isolating the variant thus induced. The 

 strain R36A has lost all the specific and distinguishing characteristics of the parent S 

 organisms and consists only of attenuated and non-encapsulated R variants. The 

 change S — » R is often a reversible one provided the R cells are not too far "degraded." 

 The reversion of the R form to its original specific type can frequently be accomplished 

 by successive animal passages or by repeated serial subculture in anti-R serum. When 

 reversion occurs under these conditions, however, the R culture invariably reverts to 

 the encapsulated form of the same specific type as that from which it was derived (11). 

 Strain R36A has become relatively fixed in the R phase and has never spontaneously 

 reverted to the Type II S form. Moreover, repeated attempts to cause it to revert 

 under the conditions just mentioned have in all instances been unsuccessful. 



The reversible conversion of S^R within the limits of a single type is quite 

 different from the transformation of one specific type of Pneumococcus into 

 another specific type through the R form. Transformation of types has never 

 been observed to occur spontaneously and has been induced experimentally 

 only by the special techniques outlined earlier in this paper. Under these 

 conditions, the enzymatic synthesis of a chemically and immunologically 

 different capsular polysaccharide is specifically oriented and selectively de- 

 termined by the specific type of S cells used as source of the transforming agent. 



In the course of the present study it was noted that the stock culture of R36 on 

 serial transfers in blood broth undergoes spontaneous dissociation giving rise to a 

 number of other R variants which can be distinguished one from another by colony 

 form. The significance of this in the present instance lies in the fact that of four 

 different variants isolated from the parent R culture only one (R36A) is susceptible to 

 the transforming action of potent extracts, while the others fail to respond and are 

 wholly inactive in this regard. The fact that differences exist in the responsiveness 

 of different R variants to the same specific stimulus cnphasizes the care that must be 

 exercised in the selection of a suitable R variant for use in experiments on trans- 

 formation. The capacity of this R strain (R36A) to respond to a variety of different 

 transforming agents is shown by the readiness with which it can be transformed to 

 Types I, III, VI, or XIV, as well as to its original type (Type II), to which, as pointed 

 out, it has never spontaneously reverted. 



Although the significance of the following fact will become apparent later on, it 

 must be mentioned here that pneumococcal cells possess an enzyme capable of de- 

 stroying the activity of the transforming principle. Indeed, this enzyme has been 



190 



