IMMUNITY AND SUSCEPTIBILITY 69 



fluence of the spleen was not greater than that of any 

 other organ in overcoming bacterial infections. 



Kanthack l found that the removal of the spleen had 

 practically no influence upon the natural immunity of 

 animals to pyocyaneus infection. 



(e) By combining two different species of bacteria^ either 

 of which, when injected alone, would be harmless or of 

 slight effect. Roger found that when animals immune 

 to malignant edema were simultaneously injected with 

 i to 2 c.cm. of a culture of Bacillus prodigiosus and the 

 bacillus of malignant edema, they would contract the 

 disease. Pawlowski found that when rabbits, which 

 are very susceptible to anthrax, were simultaneously in- 

 jected with anthrax and prodigiosus, they recovered 

 from the anthrax, as if the harmless microbe possessed 

 the power of neutralizing the products of the patho- 

 genic form. 



Giarre found that if an adult guinea-pig, which is refrac- 

 tory to infection by pneumococci, were simultaneously in- 

 oculated with diphtheria, it readily died of septicemia. 



Sometimes an apparent immunity depends upon the 

 attenuation of the culture used for inoculation, and the 

 erroneous results to which such a mistake may lead are 

 obvious. Should a culture become attenuated, its viru- 

 lence may sometimes be increased by inoculating it into 

 the most susceptible animal, then from this to a less 

 susceptible, and then to an immune animal. The viru- 

 lence of anthrax is increased by inoculation into pigeons, 

 and also by cultivation in an infusion of the tissues of 

 an animal similar to the one to be inoculated. 



It must be understood that the term "immunity" is 

 a relative one, and that while "a white rat is immune 

 against anthrax in amounts sufficiently large to kill a 

 rabbit, it is perhaps not immune against a quantity 

 sufficiently large to kill an elephant." 



It is not to be expected that such intricate phenomena 

 as these which have been mentioned could be observed 



1 Centralbl.f. Bakt. it. Parasiienk., 1892, xii., p. 227. 



