354- BIOLOGY OF PNEUMOCOCCUS 



Because of simplicity of preparation, stability, and freedom 

 from undesirable secondary action, heat-killed vaccines are pref- 

 erable to those prepared with bile, bile salts, soaps, or other sol- 

 vents or devitalizing agents. Sensitized cocci present no advan- 

 tages in immunizing properties over cells untreated with specific 

 immune serum. 



The route by which antigens are introduced into the animal 

 body affects both the kind and quantity of specific antibodies 

 called forth. Injection into the venous system is the most effective 

 method for inducing a high degree of immunity and strict type- 

 specificity of the antibodies. Injection into the peritoneal cavity, 

 into the muscles, or under the skin likewise leads to the elaboration 

 of antibodies but, owing to the respectively slower absorption of 

 antigen, there is a broadening of the specificity of the immunologi- 

 cal response. Injection of pneumococcal substance into the skin 

 stimulates the formation of antibodies but type-specificity may be 

 sacrificed for species-specificity. The introduction of antigen into 

 the bronchi by inhalation, insufflation, or injection, and also by 

 enteric paths, is even less effective in raising the level of resistance 

 or in evoking demonstrable immune substances in the circulating 

 blood. 



The age of the animal treated with immunizing agents is another 

 condition that determines the ability of animals to respond, at 

 least in a quantitative way, to antigenic stimuli, while different 

 species of animals display various physiological traits when in- 

 jected parenterally with Pneumococcus or its derivatives. 



The antagonistic effect of excessive doses of pneumococcal mate- 

 rial, particularly of the specific capsular polysaccharide, may 

 again be emphasized, since the amount of the soluble specific sub- 

 stance in a vaccine influences the development of the immune state 

 or of immune substances. 



These, then, are the several factors which condition the immuno- 

 logical behavior of animals toward substances of pneumococcal 

 origin and which qualify any definition of the term antigen. 



