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 bas 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 Metehnikoff, that the leucocytes were the only actual 
