9 



to pneumococcus broth culture there is an immediate turbidity, and 

 visible clumps quickly form, especially on gentle shaking, which 

 aggregate into a compact mass. An almost identical result, but 

 a less bulky precipitate, is obtained with a broth culture from 

 which the cocci have been removed by nitration. Thus, this 

 type of reaction, which is very specific for each serological type 

 of pneumococcus, depends on the formation of a precipitate 

 between the serum and a soluble substance in the broth. If, 

 however, the centrifuged cocci from a broth culture are resuspended 

 in salt solution, they form a compact mass with immune serum 

 similar to the above, although the soluble substance has been 

 removed with the broth. This appears to indicate that either 

 the external portion of the pneumococcus contains some of the 

 soluble substance in process of secretion, or both are of similar 

 constitution. 



The attenuated R strain agglutinates with the same serum 

 in a different manner. If broth culture is used, agglutination is 

 slow, and fine granules form which settle to the bottom of the 

 tube. A more copious deposit is formed when a thicker salt 

 solution suspension of cocci is used. In both cases, however, the 

 clumps do not aggregate into a compact mass, but can be readily 

 shaken up into a finely granular suspension. The difference in 

 character between the reactions of the II and S strains seems 

 capable of a simple explanation. Since no precipitation or 

 turbidity occurs when the serum is added to a filtered broth 

 culture of the R strain, it is obvious that the R culture does not 

 form any soluble substance, and hence there is nothing to bind 

 the agglutinated cocci into a firm mass. 



The R culture suspensions are rather less stable than the 

 smooth and, in addition, they are less specific in their agglutina- 

 bility, often showing some reaction with heterologous sera; 

 they continue, however, to react with the type serum to a higher 

 titre than with any other pneumococcal serum. 



Mode of Action of Protective Antipneumococctts 

 Serum in the Animal Body. 



The attenuation of virulent pneumococci by growth in 

 homologous immune serum in vitro is a phenomenon which is 

 probably related to the protective action of the serum in the 

 animal body and may help to explain it, though the two processes 

 are obviously not identical. In the test-tube the action of the 

 serum is shown in the altered virulence of the new generation of 

 pneumococci, hough the change is never complete in the first 

 passage through serum, the culture remaining a mixture of 

 virulent and non-virulent elements. Though pneumococci have 

 been recovered from an immunised animal at several stages 

 before their final disappearance it has not been possible actually 

 to demonstrate any change into rough colonies. In an immunised 

 animal the inoculated pneumococci have generally disappeared 

 from the peritoneal cavity within 24 hours; they remain alive 



