DISSOCIATION AND TRANSFORMATION 141 



lent composite culture was more virulent for rabbits and less re- 

 sistant to unfavorable media than was the composite strain or 

 other strains similarly obtained from the same source. Amoss iso- 

 lated by the plating method an avirulent strain from the compos- 

 ite virulent culture which had been repeatedly transferred and 

 grown in immune serum broth, bile broth, and slightly acid broth. 

 Cultures of the virulent single-cell derivative, when grown in these 

 media, also gave rise to the avirulent form. Heterologous immune 

 serum and also normal serum did not favor the change from viru- 

 lent to avirulent variants. The avirulent strains, however pro- 

 cured, were all of a single sort. They formed characteristic colo- 

 nies, showed no tendency to revert to the parent type, and did not 

 become virulent on repeated passage through mice. Serum from 

 rabbits immunized with the avirulent variants possessed aggluti- 

 nins but no protective antibodies for the parent strain. It seems 

 clear from Amoss' experiments that he had succeeded in effecting a 

 permanent degradation of a virulent Type I Pneumococcus, with a 

 loss of type-specificity, but not of species-specificity. 



The results of Reimann's 1125 study, published in the same month 

 in which Amoss' publication appeared, agreed with both Amoss' 

 and Griffith's observations. Reimann reported that cultures of 

 pneumococci from single-cell seedings, when grown in broth con- 

 taining immune serum, bile, or even normal serum, suffered a de- 

 crease in virulence and loss of type-specificity. The changes might 

 take place when the pneumococci were repeatedly grown in plain 

 broth or on blood agar, but were due to variations in individual 

 cells, rather than in the cocci of the culture as a whole. Reimann 

 preferred 2 per cent unheated blood agar to Griffith's chocolate 

 agar, and on this medium there appeared characteristic smooth 

 colonies along with others of the rough form. Cultures from S colo- 

 nies were highly virulent, had large capsules, produced soluble 

 specific substance, dissolved in bile, and were strictly type-specific. 

 Strains from R colonies were avirulent for mice, had no capsule, 

 produced no soluble specific substance, did not dissolve so readily 



