DISSOCIATION AND TRANSFORMATION 139 



take us too far afield to quote from it here, but the communication 

 is recommended to those readers who desire to learn more of the 

 philosophical aspects of the phenomenon of dissociation. 



In seeking a medium that would emphasize the differences in va- 

 riants, Sia and Chung, 1270 " 1 by the substitution of normal dog 

 blood for rabbit or horse blood in agar for plate cultures, obtained 

 such marked differences in the morphology of S and R colonies 

 that differentiation, they claimed, became extremely simple. With 

 a moderate degree of magnification (X 28), the S colonies were 

 seen to be smooth and glossy, while the R colonies, including those 

 derived from Pneumococcus Type IIS, revealed a wrinkled and 

 coarsely rough surface. The R colonies also exhibited strong he- 

 molytic properties. Sia and Chung tested the blood of guinea pig, 

 white rat, chicken, and cat, but none was so good as dog blood. 

 These authors believed that the property of dogs' blood resided in 

 the cellular elements rather than in the plasma, and probably was 

 due to hemoglobin. 



MODIFICATIONS A, B, AND C 



Blake and Trask (1923), 129 in conducting experiments similar 

 to those of Stryker, also found that growth of pneumococci in ho- 

 mologous serum resulted in a marked loss of virulence, accom- 

 panied by constant and distinct changes in agglutinative proper- 

 ties with respect both to the character of agglutination and the 

 zone of optimal reaction. The authors found the changes not to be 

 a gradual alteration of all members of a culture but, instead, there 

 appeared to be a comparatively rapid and complete change in in- 

 dividual organisms. The variants exhibited changes not only in 

 virulence and agglutinability, but also in colony appearance, by 

 means of which three modifications, called by the authors A, B, 

 and C, could be distinguished. 



In the same year, analogous observations were published by 

 Yoshioka. 1564 Typical pneumococci underwent apparently regular 

 serological modifications when maintained under unfavorable con- 



