PHAGOCYTOSIS 



279 



sinuses of the lymphnodes, and of the spleen. However, there are 

 many other cells in addition to these which may be phagocytic. The 

 writer, with Carey, 16 has observed the active phagocytosis of leprosy 

 bacilli by cells, probably of connective tissue origin, growing from 

 plants of rat spleen in plasma. Phagocytosis by the cells lining the 

 alveoli of the lungs has been observed by Briscoe. 17 This author made 

 the interesting observation that in cases of mild infection such cells 

 can free the lungs of micro-organisms entirely without aid from the 

 leukocytes of the circulating blood. It is these cells, too, which, in 

 the ordinary conditions of life, take up the inhaled particles of dust 

 and are, therefore, often spoken of as dust cells. The origin of the 

 dust cells has often been the subject of controversy. In the embryo 

 the alveoli of the lung, like the bronchi, are lined with columnar cells 

 which are transformed into flattened epithelium as the alveoli ex- 

 pand at the first inspirations after birth. These flattened cells, 

 which constitute the alveolar or dust cells, are probably of epithelial 

 origin, and as such are probably the only epithelial cells which act 

 as phagocytes under ordinary conditions. Although no positive 

 general statement is justified, we can yet say with reasonable accuracy 

 that among the phagocytic fixed tissue cells the most important are 

 the connective tissue and endothelial cells. 



The type of phagocy- 

 tosis and the variety of cell 

 which participates in it 

 seem to depend to a great 

 extent upon the nature of 

 the substance which incites 

 the process, or rather at 

 which the process is aimed. 

 Thus the large cells which, 

 in tissues, take up the lep- 

 rosy bacillus, those which 

 are characteristic of tuber- 

 culous foci, or those caused 

 by blastomycetes, or by for- 

 eign bodies, all have special 

 appearances which are suf- 

 ficiently characteristic to 

 have diagnostic value. 



However, it is difficult to determine with certainty the origin 

 of the cells which participate. The chemical nature of the substances 

 taken up, moreover, often complicates the phagocytic process in such 

 a way that different cellular elements are enlisted in succession in 

 order that the ingested substances may be disposed of. Thus tubercle 



16 Zinsser and Carey. Jour. A. M. A., March, 1912, Vol. 58. 



17 Briscoe. Jour, of Path, and Bacter., Vol. 12, 1907. 



GIANT CELL IN TUBERCULOSIS. 



