278 



INFECTION AND RESISTANCE 



BAT LEPROSY BACILLI GROUPED IN THE REMAINS OF 



DEAD SPLEEN CELLS GROWING IN PLASMA. 



Drawn after illustration in Zinsser and Carey, Journal 



of the A. M. A., Vol. 58, 1912. 



cytosis is therefore 

 an attribute of a 

 considerable num- 

 ber of different va- 

 rieties of cells. In 

 the circulating 

 blood the polynu- 

 clear leukocytes are 

 the most actively 

 motile and phago- 

 cytic elements. The 

 eosinophile cells 

 may also take up 

 foreign particles 

 and bacteria, as 

 may also the large 

 lymphocytes. The 

 small lymphocytes 

 and mast cells are 

 either entirely inac- 

 tive in this respect, or, at least, possess phagocytic powers under ex- 

 ceptional circumstances only. This does not mean, however, that 

 these last-named cells may 

 not accumulate at the point 

 of invasion nor that they 

 may not play an important 

 part in the defence of the 

 body. It is well-known, of 

 course, that, in tuberculosis 

 and a number of other con- 

 ditions, the lymphocytes 

 may form the majority of 

 the cellular elements which 

 accumulate at the site of 

 the lesion. Among the 

 fixed cells of the body it is 

 probable that phagocytosis 

 may be carried on by cells 

 of many different origins, 

 though the identification of 

 cells in tissues is often a 

 purely morphological prob- 

 lem, and therefore fraught 

 with many possibilities of 

 error. Probably the most active fixed tissue cells are the endothelial 

 cells of the blood vessels and those which line the serous cavities, the 



PHAGOCYTOSIS OF SENSITIZED PIGEON COR- 

 PUSCLES BY ALVEOLAR CELLS OF LUNG. 



Drawing made after photomicrograph pub- 

 lished by Briscoe, Journal of Path, and 

 Bact., Vol. 12, 1908. 



