ANTIGENICITY OF PNEUMOCOCCUS 351 



Rule confirmed the superiority of the subcutaneous over the oral 

 route of administration. 



Host Response 



As in all physiological processes there are periods in the devel- 

 opment of an animal when the somatic cells function more actively 

 in absorbing alien material and in creating and extruding immune 

 substances into the circulating blood. This power may be lacking 

 in very young animals, but it appears to increase as the animal 

 grows and reaches a stage of full vigor, and then to decline as the 

 metabolism of the body cells wanes. In addition to quantitative dif- 

 ferences due to age in the antibody content of serum of rabbits 

 immunized against Pneumococcus, Baumgartner (1934) 91 " 2 de- 

 tected qualitative variations as well in the antibodies elaborated by 

 young and older animals. The fact is sufficiently well established in 

 immunological practice to require no detailed discussion. 



Antagonistic Action of Soluble Specific Substance 

 In preceding chapters, mention was made of the aggressin-like 

 action of soluble specific substance, of the zonal effect observed 

 when this substance was used as an immunizing agent, and of its 

 antagonistic behavior in reactions between immune serum and 

 Pneumococcus or its derivatives. The soluble specific substance, al- 

 though non-toxic in itself, can enhance the invasive power of pneu- 

 mococci (Felton and Bailey 419 ). The phenomenon may be an addi- 

 tive effect which, in turn, may be due to some interference with the 

 natural defense mechanism of the body. Whatever the explanation 

 of this property of specific polysaccharides, it is a fact to be reck- 

 oned with in the production of active immunity, in testing the im- 

 munity established by the administration of pneumococcal anti- 

 gens, and in measuring the potency of antipneumococcic serum. 



Felton and Bailey demonstrated that the immunizing action of 

 soluble specific substance operated within certain prescribed lim- 



