118 INFECTION AND IMMUNITY. 



of the typhoid bacillus isolated from a 

 may show this increased resistance. 

 Resistance to It is an old tenet of Metchnikoff that virulent 



Phagocytosis. . . 



micro-organisms are less susceptible to phagocyto- 

 sis than avirulent. This was supposed to be due 

 to the establishment of a negative chemotaxis, 

 which consisted either in a repelling of the leuco- 

 cytes or in their failure to be attracted to the bac- 

 teria. In 1892 Massart reported that leucocytes 

 were negative chemotactically to virulent strains of 

 the organisms of anthrax, chicken cholera, swine 

 plague, and to B. pyocyaneus and Vibrio metchni- 

 kovi, and that they were taken up by leucocytes in 

 the animal experiment to a much less extent than 

 avirulent strains of the same organisms. The same 

 condition was noted in relation to staphylococci 

 (van der Velde, Kocher, Taval). Since phagocy- 

 tosis has been studied more extensively under arti- 

 ficial conditions, the same phenomenon has been 

 noted in relation to other organisms, as the strepto- 

 coccus (Hektoen and Euediger, Bordet, etc.), 

 pneumococcus (Eosenow), typhoid and paraty- 

 phoid bacilli (Neufeld and Hiine, Hektoen), the 

 colon bacillus (Beattie), the meningococcus (Flex- 

 ner), and others. In African tick fever, Levaditi 

 and Roche noted the presence of spirillicidal and 

 opsonic substances (those favoring phagocytosis) 

 following the first attack of fever, but they 

 appeared to be effective only on the spirilla which 

 were present in the blood during the first attack. 

 By the time the second attack occurred the organ- 

 isms had acquired a resistance to these substances 

 which they retained during several passages 

 through rats subsequently. It would seem that 

 this acquired resistance on the part of the organ- 



