480 BIOLOGY OF PNEUMOCOCCUS 



introduced into the animal body stimulate the production of spe- 

 cific antibodies in even less time than do true toxins or filtrable 

 viruses ; but while these specific antibodies may guard the indi- 

 vidual against infection by Pneumococcus, the same evidence shows 

 that the immunity so induced, when at all effective, is specific only 

 for the serological type of the antigen employed and at best is dis- 

 appointingly transient. 



In the chapters on antigenicity (X), antibodies (XI), and host 

 response to antigenic action of Pneumococcus (XII), the facts 

 presented would seem to warrant the conclusion that antigens rep- 

 resenting the components of the pneumococcal cell as they exist in 

 the cell at the height of vital function are, as a rule, the most ef- 

 fective in establishing the immune state. With Pneumococcus as 

 with other bacterial material, attempts by means of physical or 

 chemical agents to rob the antigen of undesirable properties or to 

 isolate or concentrate the antigenic principles frequently so dis- 

 rupt or denature the constituents of the cell as to deprive the 

 agent of its immunizing properties. However, the protection of the 

 individual or of groups of individuals against pneumococcal infec- 

 tion is often so desirable or so urgent that, bearing in mind the 

 limitations of the practice, the administration of vaccinal agents 

 made from pneumococci is fully justified. The complications pre- 

 sented by the type-specific action of pneumococcal antigens, 

 changes in the prevalent variety of serological types, and the tem- 

 porary nature of the protection conferred only spur the immu- 

 nologist to further endeavor to increase the effectiveness of pneu- 

 mococcal vaccines. 



Basically the antigens employed for the production of active 

 immunity in experimental animals and man fall into four general 

 groups. 



1. Saline suspensions of pneumococci devitalized by heat, formalin, 

 phenol, soaps, or other physical or chemical agents. Vaccines of this 

 kind may be assumed to represent all the constituents of the cell in 

 their natural state, making allowance for such alterations in intrinsic 



