The question of the stability of the R and S characters will 

 be considered later. 



In order to produce the variant from a normal strain through 

 the influence of specific serum, it is necessary that growth should 

 occur. No alteration has been observed on plating a culture 

 that has remained in contact with the specific serum at ice- 

 chest temperature, or has been shaken with the serum at 

 room temperature. The variant, therefore, is a new generation 

 in the serum and not one of the original pneumococci altered 

 by contact with the serum. This point is of importance when 

 one compares the action of the serum upon the pneumococci in 

 the animal body and in the test tube. 



Concentrated serum is not essential for the production of R 

 forms. A dilution of 1 in 256 has caused a partial change of a 

 smooth culture into a rough even with a single treatment. In 

 addition, the blood of a mouse, which has received a dose of 

 0-2 c.c. of serum, has been collected about 18 hours later, and 

 used as a culture medium. The pneumococci sown into it grew 

 as in a dilute agglutinating serum, and from one such culture, 

 after being incubated a night and then plated, several rough 

 colonies were produced. 



Heterologous sera, as already stated, have generally no power 

 to produce rough colonies from a smooth culture and numerous 

 experiments have given negative results, even after several 

 passages. I have, however, found one exceptional instance. A 

 Type I. strain grown in a Type II. serum produced rough colonies 

 when plated: these remained rough after many generations in 

 blood broth. Until then it had seemed that the production of 

 rough colonies in a given serum might serve as a test of the 

 serological type. For example, the atypical II. A and II. B strains, 

 which are believed by the American observers to be related to 

 Type II., were grown in undiluted Type II. serum. Both strains 

 grew uniformly and not in chains, thus showing the absence of 

 agglutinins for them, and after five consecutive passages in 

 Type II. serum the colonies remained of the normal smooth 

 type. I have recorded elsewhere* evidence that the so-called 

 atypical Type II. strains are serologically distinct from Type II. 



Description of the R and S Forms of Pneumococcus 



Colonies. 



All the serological varieties of pneumococci with the exception 

 of Type III. yield on the same medium colonies which are indis- 

 tinguishable. There is, however, only a difference in degree 

 between the Type III. colonies and the others, and sometimes the 

 colonies of Type II. and the atypical strains of Group IV. are 

 equally large and watery. The following description of the 

 normal type of colony applies only to strains which have been 



* Reports on Pub. Health and Med. Subjects, Ministry of Health, No. 13, 

 1922. 



