THEORIES OF IMMUNITY. 



polymorphonuclear leucocytes from the marrow, 

 and in all cases of severe infection there is the 

 further stimulative effect which leads cells in 

 various parts to divide. Either this stimulation 

 is part of a reparative process, or it is to be 

 looked on as the result of injury due, say, to cir- 

 culating poisons. The fact that in relation to 

 one aspect of the process, namely, the poly mo r- 

 phonucleate reaction, the effect is often to in- 

 crease at a given point the available number of 

 cells capable of playing the part of phagocytes 

 leads one to think that all these tissue changes 

 may be of the nature of an exaggeration of nor- 

 mal functions, the general effect of which ex- 

 aggeration is to have a beneficial effect. It is to 



So 



be noted as a very important point in this pro- 

 cess that most of the distant effects must be due, 

 even in the case of bacteria which in vitro do 

 not produce soluble poisons, to the circulation of 

 soluble toxines, unless — which is possible — we 

 consider bacteria capable of exerting purely 

 physical influences. Connected with these is 

 the other very important fact that embryonic 

 activity may be dissociated from any actual 

 phagocytosis on the part of the proliferating 



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