60 THE DEFENSIVE FORCES OF THE MACROORGANISM 



Special stress is laid upon the fact that these results were obtained 

 in immune animals, as it could only be shown in this way that the 

 leukocytes are capable of taking up not only living but also virulent 

 bacteria, i. e., bacteria which in the non-immune organism would 

 have produced a general infection. 



That living foreign cells are subject to phagocytosis is also well 

 shown by the following experiments : If a guinea-pig is injected intra- 

 peritoneally with goose's blood containing the spirillum of Sacharoff, 

 which produces a septicemic infection in geese, and if a drop of the 

 exudate is then examined under the microscope, phagocytosis of the 

 spirilla in this case by macrophages can be observed directly, and 

 it will be seen that many of the organisms are quite motile yet with 

 their free ends, while the remainder of the parasites has already 

 been taken up by the cells. 



Destruction of Bacteria by Phagocytosis. While there can thus be 

 no doubt that both micropbages and macrophages can take up living 

 foreign cells the next question of importance is, What happens to the 

 organisms after they have been taken up? Two possibilities, of course, 

 suggest themselves. We may imagine, on the one hand, that the 

 phagocyte destroys the bacteria, and a priori this would seem the 

 most natural thing to expect. On the other hand the possibility at 

 least must be borne in mind that the bacteria may destroy the 

 phagocytes. If this were to happen we could readily understand 

 that phagocytosis might at times be of some danger to the animal, 

 for we could see that a chance might thus be afforded for a wider 

 distribution of the parasites. The possibility of such an occurrence 

 is suggested by the fact that the phagocytosis of tubercle bacilli by 

 giant cells, for example, usually leads to the destruction of the latter 

 and not necessarily to the death of the bacilli. It must be admitted, 

 however, that the greater weight of the evidence goes to show that 

 sooner or later the ingested organisms are killed. The intracellular 

 granular degeneration of bacteria which one can observe directly 

 under the microscope certainly points in that direction. 



Of the manner in which the destruction of the bacteria is brought 

 about we are as yet in comparative ignorance. Recent research 

 seems to show that the leukocytes contain special endolysins which 

 may be operative in this direction. This is really what one would 

 expect, remembering that the proteolytic enzymes of the cell can 

 hardly exercise any germicidal action, and that in many of the lower 



