IMMUNITY 83 



upon the nature of the infection. In diphtheria, 

 which is an example of a toxemia, antitoxin plays the 

 leading part, while the phagocytes perform a subordinate 

 function in destroying the germs which are producing the 

 toxin. In suppurations, as in gonococcus or staphylo- 

 coccus infections, in which the toxins are of secondary 

 importance in the production of the diseased processes, 

 phagocytes and bacteriolysins bear the burden of the 

 fight. Rabbits and dogs are both relatively immune to 

 pneumonia, but the germs develop more readily in the 

 rabbit than in the dog. The rabbit, however, is less 

 susceptible to the poison than the dog, which would 

 indicate that in the rabbit the antitoxin was the basis 

 of immunity, while in dogs who are susceptible to the 

 toxins, but on whom the germs do not thrive, the im- 

 munity is more than likely due to the phagocytosis or 

 the bactericidal bodies. 



Briefly summarized, the part performed by the va- 

 rious factors in immunity are as follows : The phagocytes 

 or white blood-corpuscles leave the blood-vessels and 

 flock to the site of infection or the local lesion, there to 

 devour and destroy the invading germs. 



The antitoxins neutralize the toxins produced by the 

 germs. If the toxins are excreted by the germs and taken 

 up by the blood, as in diphtheria, it does this unaided. 

 If, however, as in cholera, the germs themselves enter 

 the blood and carry their poisons within their bodies, 

 the bacteriolysins must, by dissolving the germs, set 



