PHAGOCYTOSIS. 175 



especially well adapted for the study of phagocytosis in vivo. The following 

 experiment of MetschnikofT may serve as a type. 



A guinea-pig receives an intraperitoneal injection of goose's blood. Immediately 

 following this, the leucocytes disappear from the peritoneal fluid. This is due partly to 

 a destruction of leucocytes (Phagolysis) and partly because the leucocytes are repulsed 

 and settle upon the peritoneal wall. In one to two hours this so-called negative phase 

 is overcome and there is an increase of the leucocytes, especially of the macrophages in 

 the exudate (Hyperleucocytosis). Now, the leucocytes can be seen sending forth short 

 protoplasmic processes pseudopodia, by means of which the erythrocytes are drawn 

 into the phagocytes. After a short time the macrophages are filled with the erythrocytes. 

 At first the ingested cells appear normal ; gradually, however, they undergo changes, which 

 are clearly visible in the unstained specimen, indicative of a disintegrating process, 

 within the body of the phagocytes. 



The same phenomenon as described for goose's erythrocytes can also be 

 observed with bacterial bodies. 



In order to exclude the possible bactericidal influences of the serum, it is advisable 

 when one is working with bacteria which are readily destroyed as cholera vibrios, to 

 previously induce a hyperleucocytosis in the peritoneal cavity. The guinea-pig receives 

 an intraperitoneal injection of 10 to 20 c.c. of sterile bouillon or aleuronatsolution. In 

 about twelve hours hyperleucocytosis takes place, and a capillary pipette inserted into 

 the peritoneal cavity will withdraw a thick and turbid exudate. 



If this animal is injected intraperitoneally with bacteria, and a smear of 

 the peritoneal fluid made a short time after the inoculation, the bacteria 

 will be seen lying within the microphages. This important fact has been 

 variously interpreted. Pfeiffer and his pupils claim that the bacteria are 

 first destroyed or their virulence greatly diminished by the bactericidal 

 power of the serum and exudate, and "that the phagocytes act only as recepta- 

 cles for these already destroyed bacteria. Metschnikoff believes that the 

 phagocytes take up the living bacteria and destroy them, thus representing 

 these cells as the most important weapons of the organism in its protection 

 against infection. 



" Every time an organism that has lost its susceptibility toward a partic- 

 ular infective agent, either on account of a natural born immunity or an 

 artificially attained one, comes into conflict with this infective agent, a 

 struggle arises between the latter and the phagocytes of the threatened 

 individual. It is the phagocytes that appear as victors, since they take up 

 the bacteria into their protoplasmic bodies and digest them, thus forever 

 depriving them of their power for evil." (Metschnikoff cited by Levaditi). 



Critically considered, there can be no doubt that the phagocytes are in 

 principle capable of dealing with living virulent bacteria. At the same time 

 one must observe that the opsonins and bacteriotropins of the serum soon 

 to be discussed, in most instances previously modify the living bacteria in 

 some way at present still unknown. That, however, the phagocytes can 

 ingest bacteria or protozoa which are alive and active, has been demonstrated 



