248 PHAGOCYTES OF THE PERITONEUM AND LUNG 



suitable conditions any phagocyte can ingest any abnormal body 

 of suitable size. 



Under certain conditions there may be traced a remarkable 

 sequence in the advent of various phagocytes to an infected area, 

 which almost suggests a symbiosis of the nomadic cells. Thus, 

 when a culture of a bacteria is injected into the peritoneum of the 

 lower animals, a very definite sequence of events takes place. 

 The peritoneal fluid normally contains some small mononuclear 

 cells, probably of endothelial origin, and a few polynuclears. 

 For an hour or so after the injection these cells are diminished in 

 numbers, and the eosinophiles disappear altogether. The exact 

 cause of this diminution is not quite clear. It may be due to the 

 dilution of the peritoneal fluid by the solution injected, or to the 

 destruction of the cells, or to their clumping together on the 

 omentum, but in any case is not due to negative chemotaxis. For 

 the next two hours or so there is a gradual increase of the 

 polynuclears, at the end of that time an influx of small mono- 

 nuclears, until in about six hours these and the polynuclears are 

 present in approximately equal numbers. After this the mono- 

 nuclears (which are probably budded off from the peritoneal 

 cells, and are thus endothelial in origin) gradually become larger, 

 forming what Metchnikoff calls macrophages ; then the fluid 

 slowly becomes concentrated, and the polynuclears gradually 

 disappear, many being ingested by the large mononuclears. 

 Finally these too disappear, but it takes about a fortnight for the 

 animal to revert to its normal condition. Both varieties of cells 

 endothelial and polynuclear take part in ingesting the cocci. 



Briscoe has shown that a remarkable series of processes also 

 occurs when organisms, etc., are injected into the alveoli of the 

 lungs. It varies according to the substance injected, and we 

 may take the result of the injection of the potato bacillus as an 

 example. In the first hour and a half phagocytosis is very active, 

 the bacilli being taken up exclusively by the pre-existing alveolar 

 epithelial cells. Up to this time practically no polynuclears have 

 made their appearance, but they now commence to be attracted 

 into the alveoli, where they occur in large numbers for about 

 twenty-four hours. They take, however, but a small share in the 

 phagocytosis of the bacteria, and are themselves taken up by the 

 alveolar cells. Some proliferation of these latter cells occurs, 

 and the eosinophiles increase for the first twenty-four hours, and 

 then gradually diminish. We cannot trace the reason for this 



