444 BIOLOGY OF PNEUMOCOCCUS 



closely the state of the antigen approaches that of the vigorous, 

 living, virulent cell, the greater the specificity and the complete- 

 ness, within certain limits, of the immunity and of the antibodies 

 evoked. The robust organism with its protein and carbohydrate 

 constituents in fully developed and unaltered condition exerts the 

 greatest antigenic action. The cell should be living, or devitalized 

 at the peak of its anabolic activities by heat or by such chemical 

 agents as rob the bacterium of the ability to propagate without 

 disturbing its chemical integrity. The greater the mass, within 

 certain limiting zones, the more energetic the specific antigenic 

 stimulation; while the proper spacing of injections and the route 

 by which the antigen enters the body may affect the specificity and 

 the quantity of antibodies produced. 



The protein of the pneumococcal cell is antigenic only in the 

 sense that its administration by parenteral routes results in the 

 appearance of humoral antibodies specific for the bacterial spe- 

 cies and not for the serological type of the organism injected. The 

 capsular polysaccharide, besides orienting the antigenic action 

 of its conjugated protein when its molecular configuration is un- 

 disturbed, is antigenic in itself, and it is this fraction of the pneu- 

 mococcal cell that determines the type-specificity of the immune 

 response. The somatic carbohydrate — the C Fraction — if it has 

 any antigenic action, apparently has a subordinate and as yet 

 unknown share in the immunizing action of Pneumococcus. 



In an animal of a susceptible species, unaffected by any debili- 

 tating condition, the parenteral introduction and, to a much less 

 degree, the oral administration of properly chosen pneumococcal 

 antigens, decreases susceptibility to pneumococcal infection and 

 arouses physiological functions latent in the cells of the body. 

 These functions result in the extrusion into the circulation of sub- 

 stances corresponding in type to the kind of antigen administered, 

 and demonstrable and measurable by the various serological reac- 

 tions. In addition to the appearance of humoral antibodies, the 

 somatic cells undergo changes in reactivity to pneumococcal ma- 



