PHAGOCYTOSIS 



255 



body against invaders. The point is one of theoretical interest 

 rather than of practical importance, and we have already pointed 

 out that the complement is apparently used up in its activity, and not 

 set free to attack other molecules, as is the case with the enzymes. 

 Another minor point is that Metchnikoff seems to regard the 

 setting free of cytase as only occurring when the mother cell is 

 dissolved, whereas most of the bacteriologists who admit the 

 origin of alexin from leucocytes regard it as a product of its 

 secretory activity. The point has been referred to before. 

 Metchnikoff explains the phenomena which occur in immunized 



or. 



C 



FIG. 55. PROCESS OF ABSORPTION OF ANTHRAX BACILLI IN THE LEUCO- 

 CYTES OF THE PIGEON. (Metchnikoff.) 



(Showing various stages of alteration of the bacillus whilst in the protoplasm 

 of the leucocytes.) 



as opposed to normal animals in this way : We will take the 

 absorption of bird's corpuscles from the peritoneum as an 

 example. When the injection takes place into normal animals, 

 there is no extracellular destruction of the corpuscles (haemolysis), 

 because there is no cytase free in the peritoneal fluid, no cor- 

 puscles having been broken down ; the corpuscles are taken up 

 by the phagocytes, but with some difficulty, since they have not 

 been prepared in any way for the process. When a second or 

 third injection is given, some haemolysis occurs, and this is 

 because the cells of the peritoneum are broken down by the 

 brusque introduction of the corpuscles ; this breaking down is 

 termed phagolysis, and is regarded as being a necessary pre- 

 liminary to the liberation of the cytase. The fresh leucocytes 

 which arrive now proceed to ingest the corpuscles with great 



