HOST RESPONSE TO ANTIGENIC ACTION 445 



terials. Of the immune substances engendered, the agglutinins ag- 

 glomerate the cocci and facilitate their removal from the circu- 

 lating blood and the precipitins combine with the polysaccharide 

 present in the capsule or released in the disintegration of the bac- 

 terial cell, while the opsonins render the organisms susceptible to 

 the phagocytic action of the leucocytes and of certain of the fixed 

 cells of the body. 



The immunity thus established by artificial means may become 

 apparent within the space of a few days after the administration 

 of antigen and may persist for longer or shorter periods depend- 

 ing upon the total amount of antigenic material injected, the 

 spacing and repetition of the injections, and the ability of the 

 tissues to continue their special functions. Immunity to Pneumo- 

 coccus is, at best, a transient condition, and unless the tissues are 

 fortified by continued specific stimulation, the antibodies thus ar- 

 tificially induced shortly disappear from the blood and the animal 

 again becomes vulnerable to the pathogenic action of Pneumo- 

 coccus. 



PASSIVE IMMUNITY 



The blood or serum of an immune animal, whether transferred 

 through the placental circulation or artificially injected into the 

 body of a susceptible animal, carries its complement of antibodies 

 that serve to convert susceptibility into resistance; the degree of 

 resistance depends upon the potency of the serum in immune sub- 

 stances, the volume of serum, the route and frequency of adminis- 

 tration, and the capacity of the recipient to utilize the antibodies 

 so conferred. In the passively immunized animal, the type of im- 

 munity acquired corresponds in specificity to the immunity of the 

 donor. 



References to the inheritance of immunity to pneumococcal in- 

 fection are singularly rare. By inference, it might be assumed 

 from the work of Irwin and Hughes 670 that native resistance may 

 be increased by selective breeding, but in that case the ability of 



