176 PHAGOCYTOSIS OPSONINS AND BACTERIOTROPINS. 



by Metschnikoff's school. Phagocytosis experiments were undertaken 

 with motile bacteria and spirilla. On microscopical examination it was 

 seen that a phagocyte was in the act of taking up a spirillum, part of which 

 was engulfed by the cell while the remainder was still outside of the cell and 

 continuing its active motility. 



Not in all cases does phagocytosis of bacteria lead to destruction of the ingested 

 microbes. More recently different experiments seem to prove that simple phagocytosis 

 of bacteria must not be considered as identical with death of the same. Furthermore, 

 the exudate from cases of anthrax in which the bacilli lie within the leucocytes, can still 

 produce fatal anthrax when inoculated into animals. 



Vital Staining A more exact understanding of the bio-chemical nature of 

 with Neutral phagocytic digestion has been offered by the method of vital 

 Red. staining with neutral red. 



Neutral red (used as a i per cent, solution in isotonic saline) is a chemical dye which 

 stains only dead cells and not living ones. If live bacteria and phagocytes are brought 

 into contact in hanging drop preparations (and a drop of the stain is added at various 

 intervals to a different mixture), the first slide shows the extracellular living bacteria 

 unstained, while of the intracellular bacteria, a part remains unstained and the other 

 colored red. 



The later the mixtures are stained, the more numerous are the intracellular red stained 

 bacteria, showing that the injected micro-organisms remain alive for a short time, and then 

 die. The intracellular bacteria retain their stain as long as the phagocytes themselves 

 remain alive. Later, when the phagocytes die, the formerly red bacteria lose their 

 stain. Metschnikoff's explanation of the red staining process is that during the act of 

 digestion by the phagocytes, an acid ferment is liberated which gives the color reaction 

 with the neutral red. 



For many years Metschnikoff's phagocytic theory opposed the conception 

 of Ehrlich and also Pfeiffer in relation to the importance of amboceptor and 

 complement in the mechanism of immunity. It would be out of place here 

 to review the various experiments performed and offered on each side in 

 explanation of its standpoint. Suffice it to say that Metschnikoff denied the 

 existence of free complement within the animal organism. He moreover 

 claimed that the complement was found normally only in the phagocytes and 

 hence called it "cytase," differentiating the two phagocyte groups as "micro- 

 and macrocytase." The "cytase" is liberated when the phagocytes are 

 broken up. The amboceptors are considered as split products of the 

 phagocytes and known by Metschnikoff as "fixators." 



2. Opsonins. 



In recent years the closer relationship which has arisen between the fol- 

 lowers of phagocytic and humoral theories was made possible by the fact that 

 Denys and Leclef, Leishmann, Wright and Douglas and others, demonstrated 

 that phagocytosis occurs in most cases only in the presence of serum. If the 

 phagocytes are thoroughly washed, so that they are entirely serum-free, 



