INFECTION, IMMUNITY, AND RECOVERY. 121 



Their source must apparently be attributed to the cells, 

 but probably certain cells only produce them. The red 

 blood-cells, for instance, seem rather to destroy than to 

 increase them. The nuclein derived from the cells, al- 

 though it has a general bactericidal action, and may enter 

 into the alexines, yet as it has different properties it can- 

 not itself be one of these bodies. The cells which have 

 abundant nuclear substance, such as the leucocytes and 

 lymph-cells, seem especially to be a source of the alex- 

 ines. Buchner and others have found that through 

 the irritation of bacterial filtrates the leucocytes were 

 attracted in great numbers to the region of injection, 

 and that the fluid here, which was rich in leucocytes, 

 was more bactericidal than that of the blood-serum 

 elsewhere. The same fluid acted also more perfectly 

 when it contained numbers of leucocytes than when 

 they were filtered off. Substances similar to the alex- 

 ines are apparently derived from the leucocytes, and 

 their attraction to the injected area gives to that loca- 

 tion greater protective power. Some claim to have 

 demonstrated that along with increased leucocytosis 

 there is a general increase in the alexines in the blood, 

 still it has not yet been positively established that the 

 alexines are derived solely from the leucocytes, nor 

 from all leucocytes, and a mere increase in them does 

 not always mean an increase in alexines. The attrac- 

 tion between the leucocytes and the bacteria is due to 

 the chemical attraction between them and the bacterial 

 body substance and its poisons. Some chemical sub- 

 stances not derived from bacteria have this quality 

 also, called positive chemotaxis, while others repel the 

 leucocytes negative chemotaxis. The original theory 

 of Metchnikoff, that the leucocytes were the only actual 



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