president's address — SECTION L. 267 



exudate rich in leiicocytes, at fir^it chieflv cf the polynuclear 

 variety, with a few lymphocytes and eosinophils, but after some 

 hours there appear much larger wandering cells — macrophages of 

 Metchnikcff — which equal or even exceed the number cf poly- 

 nu clears. 



By this means the process of phagocytosis of bacteria in vivo 

 can bei studied by withdrawing a little of the exudate at conveni- 

 ent intervals after experimental infection, and also in vitro by 

 withdrawing some of the exudate and making a hanging-drop 

 preparation which is kept at the body temperature, inoculated with 

 a bacterial culture, and observed under the microscope at frequent 

 intervals. Any effect of the peritoneal exudate in which the cells 

 are suspended can be eliminated by adding a little normal saline 

 solution, centrifuging, removing the cells, washing, and suspending 

 them in fresh saline. 



The other method, move commonly adopted by Wright, is to 

 take a little blood in citrated saline solution to prevent clotting, 

 centrifuge it, remove the supernatant liquid, and then carefully 

 pipette off the " leucocytic cream." The leucocytes are again 

 washed in saline, centrifuged, and re-suspended in saline; the 

 bacterial culture is added in minute quantity, and the mixture 

 incubated for a short time. A smear is then made on a slide, 

 fixed, stained, and examined, and the amount of phagocytosis, if 

 any, can be determined by microscopic examination. 



By these and similar methods the characteristic features of the 

 phagocytic action of leucocytes ^nd other wandering cells have 

 been made out. 



Time forbids a consideration of the physiological role of phago- 

 cytes; suffice it to mention — 



(1) their amoeboid powers; 



(2) the phenomenon of chemiotaxis by which various foreign 



siibstances attract cr repel them; 



This can be well shown by inserting two capillary tubes under 

 the skin of a rabbit, both containing nutritive broth medium, but 

 in the one case the medium inoculated with living staphylococci 

 whilst the other is sterile. Removed after 24 hours, the inoculated 

 tubes contains a turbid fluid containing very numerous polynuclear 

 leucocytes, whilst the fluid in the other tube remains clear. If, 

 instea,d of staphylococci, the tube had been sown with viriden^ 

 anthrax bacilli, there would have been few or no leucocytes but 

 a great multiplication of the anthrax bacilli, for the virulence of 

 anthrax consists in large measi.ue in its power to repel and inhibit 

 phagocytes. 



(3) their power of ingesting foreign cells and particles, well- 



shown in vitro by Wright's method; 



