1 66 THE PRINCIPLES OF IMMUNOLOGY 



phagocyted, the ingestion of these objects and in the case of living 

 objects their death ; finally the digestion of bacteria and other suitable 

 objects. The approach of the cells and the phagocytable objects is, 

 according to Mesnil and his co-workers and also Levaditi, due to a 

 physical chemical reaction and not dependent on the life of the leu- 

 cocyte. If leucocytes are injured by heat to 45, 50 or 60 C., by refrig- 

 erator temperature, by shaking, by grinding, and then mixed with bacteria 

 and inactivated immune serum, the bacteria become clumped about 

 the leucocytes. This reaction may be observed even if the tubes are 

 laid in melting ice. The leucocytes that have been killed or paralyzed 

 will not ingest the bacteria. The " anchoring " of leucocytes and 

 bacteria will not occur unless specific opsonin is present in the serum. 

 It occurs with fragments of leucocytes as well as other cells of the 

 leucocyte series, such as myelocytes and myeloblasts. Thus the affinity 

 may be expressed as existing between the protoplasm of the phagocytic 

 cell and the sensitized bacteria or other phagocytable object. 



Although actual ingestion of objects may be shown in the case of 

 artificial amebae it does not occur in the leucocyte unless the cell is 

 alive and in possession of its capacity to project pseudopodia. Hence 

 this stage of phagocytosis must be bound up with the life processes of 

 the phagocyte. 



From the earlier studies of Metchnikoff it has been known that the 

 bacteria, after phagocytosis, are killed and digested. The influence 

 of the blood fluids in this phenomenon has been the subject of much 

 study and conflicting results. Metchnikoff and his co-workers were of 

 the opinion that the leucocytes contain complement, which, as has been 

 shown in previous chapters, is required for the action of bactericidal 

 and bacteriolytic amboceptors. They believed that this complement is 

 liberated only upon the destruction of the leucocytes as seen in phag- 

 olysis for they were unable to find complement in plasma. They inter- 

 preted the presence of complement in serum as due to the death of the 

 leucocytes during clotting of the blood. This interpretation has been 

 combated by numerous observers who have been able to demonstrate 

 complement in plasma. In support of the conception that the death of 

 the bacteria is due to completion of the bactericidal amboceptor-antigen 

 complex by complement in the leucocyte, is Bordet's work with cholera 

 vibrios. Using immune sera which contained bacteriolytic amboceptor, 

 he found no lysis except in those bacteria that were within phagocytic 

 cells. As opposed to this conception, the work of Neufeld and his 

 collaborators has shown that sera may be richly opsonic without con- 

 taining lytic amboceptors, and in these instances the bacteria are 

 destroyed and digested by the phagocytes. The destruction varies with 

 different organisms and with the virulence of the organisms, the more 

 virulent being less readily killed than the avirulent strains. Bacteria 

 may be cultivated on artificial media after having been ingested, a 

 certain amount of time being necessary to kill the organisms. The 

 act of digestion is closely bound up with that of killing the organisms. 

 The presence of a proteolytic ferment in leucocytes has been known 



