CELLULAR RESISTANCE 155 



removed from the circulation by endothelial cells lining blood-vessels. 

 Microphages may also play a large part in the removal of tissue detritus 

 and may take up pigment as in malaria. 



Experimental Demonstration. The experimental demonstration of phago- 

 cytosis in mammals is comparatively simple, as the following experiment from 

 Metchnikoff will show. The blood of a bird, such as goose, hen or pigeon, is 

 selected because of the fact that the nucleated erythrocytes are easily distinguished 

 from those of mammals. Defibrinated bird blood mixed with equal parts salt 

 solution is injected (about 3.0 c.c.) into the peritoneum of a healthy guinea-pig. 

 Material is removed for study by means' of finely drawn out glass pipettes, drops 

 being placed on slides for study with or without subsequent staining. Within 

 the first hour the leucocytes seem to have disappeared from the peritoneum. 



The disappearance is particularly striking when bacteria are injected and 

 was interpreted by Metchnikoff as a destruction of the phagocytic cells, a 

 phenomenon which he called phagolysis. At the end of from one to two hours 

 exudate may be withdrawn which shows numerous cells, particularly macrophages. 

 The macrophages show ingestion of the nucleated erythrocytes and at from 

 twenty-four to forty-eight hours exhibit digestive vacuoles and partial digestion 

 of the erythrocytes. 



At the end of three days the digestion is practically complete. 

 Metchnikoff has shown that immunization will definitely limit the ap- 

 pearance of phagolysis. Sanarelli, however, maintains that the disap- 

 pearance of the leucocytes is not due to phagolysis but rather to the 

 fact that the leucocytes of the peritoneal cavity and of the blood 

 accumulate in the epiploic appendages into which the bacteria are 

 likely to be carried by the lymphatic stream. Here, he asserts, bac- 

 teriolysis and phagocytosis progress actively. Hence the disappearance 

 of the cells from the exudate. 



A similar experiment may be performed with a suspension of pigment, as 

 for example 5.0 c.c. finely-divided suspension of cinnabar (red mercuric oxide). 

 This shows no digestion but active phagocytosis and a rapid transfer to re- 

 gional lymph-nodes. 



Phagocytosis of bacteria may be very well demonstrated with colon bacilli. 

 It is desirable in this instance to excite some exudation before the introduction 

 of the colon bacilli. This may be produced by injecting about twelve hours 

 previously 10.0 c.c. sterile bouillon or aleuronat suspension. This may be done 

 in the evening and the following morning the guinea-pig is ready for the injection 

 of a 24-hour bouillon culture or a 24-hour slant agar culture suspended in salt 

 solution. The subsequent phenomena are similar to those following the injection 

 of bird blood. 



The Mechanism of Phagocytosis. In earlier experiments of this 

 sort several questions as to the mechanism of the process arose. That 

 the bacteria do not actively penetrate into the phagocytes has been 

 demonstrated by direct observation of the ameboid action of the cells 

 and is concluded also by analogy from the fact that non-motile bacteria, 

 non-motile cells, such as erythrocytes, and inert bodies, such as cinna- 

 bar, are readily ingested by the phagocytic cells. That the bacteria are 

 not killed before ingestion is shown by the fact that cultures may be 

 successful in the case of anthrax bacilli shortly after they have been 

 taken up by phagocytes. This may also be illustrated by the following 

 experiment with the use of neutral red as a vital stain. This stains only 

 dead cells and imparts no color to living cells. A warm hanging drop 

 preparation of the exudate from a guinea-pig injected with colon 



