IMMUNITY AND SUSCEPTIBILITY. 105 



Thus through a long and somewhat wearying journey 

 we are led back again to the leukocytes, and urged to 

 view them not as phagocytes, but as alexocytes, whose 

 powers lie not in their capacity for intracellular digestion 

 and destruction of bacteria, but in the secretion and 

 liberation of the germicidal substances. 



However, the occurrence of germicidal substances in 

 the blood, although bacteria of disease may be destroyed 

 by them, will not explain the phenomena of immunity. 

 The rat is immune to diphtheria not only because its 

 blood will destroy diphtheria bacilli, but also because the 

 rat is able to endure without injury the toxin of the diph- 

 theria bacillus. Enormous doses of strong diphtheria 

 toxin produce only a slight local reaction in white rats — 

 an endurance not to be explained either by phagocytosis 

 or the germicidal action of the blood, so that the essence 

 of immunity is not contained in either. 



III. The Presence of Antitoxin. — The term anti- 

 toxin is used to express a peculiar protective energy 

 which is manifested by the blood serum of animals that 

 have been subjected to forced artificial immunization. 

 Antitoxins rarely occur in the blood of normal animals. 

 The facts and phenomena concerning antitoxin will be 

 considered in a more appropriate place, but as it is possible 

 that they have something to do with natural immunity a 

 few words with regard to them must precede the chief 

 consideration of the subject. 



Finding that neither the destruction of bacteria by 

 phagocytes nor their attenuation or destruction by the 

 body humors can explain immunity to toxins, we must 

 next inquire whether the bacteria-destroying principles 

 of the blood are also toxin-destroying substances. 



Ogata and Jasuhara 1 found that injection of the blood 

 of a frog or of a rat into a susceptible animal which had 

 been inoculated with a virulent culture of the anthrax 

 bacillus will restrain the development of the bacteria 

 and prevent the death of the inoculated animal. Beh- 



1 Centralbl.f. Bakt. u. Parasitenk., ix., p. 25. 



