IMMUNITY 



191 



The supporters of the humoral theory consider that in 

 immunity the body-fluids (serum, exudates, &c.) possess or 

 acquire destructive properties independent of the cells ; that 

 there is a non-phagocytic destruction of bacteria (and poisons), 

 and that even when this destruction appears to be completed 

 in the interior of the leucocytes, the role of the latter is limited 

 to seizing and absorbing bacteria already killed. 



Of course the antagonism between these two standpoints is 

 not irreconcilable, and intermediate theories exist. The 

 priority of the cells, however, as compared with the fluids 



Fig. 63. — Phagocytosis of 

 the red corpuscles of the 

 goose by the phagocytes 

 of the snail. (Melch- 

 nikoff.) 



Fig. 64. — Intracellular (phagocytic) diges- 

 tion in an intestinal cell of Planaria. 

 ^Metchnikoff. ) 



independent of the cells, is still the subject of dispute ; no 

 theory succeeds in explaining the facts of immunity without 

 acknowledging the activity of the phagocytes and the im- 

 portance of intracellular digestion. 



The humoral theory first took the field with claims or 

 aspirations to be a " chemical " theory, when some at least of 

 the phenomena of immunity were successfully reproduced out- 



