308 INFECTION AND IMMUNITY. 



Metchnikoff divides the phagocytic cells of ver- 

 and P h"| r e s " tebrates into the macrophages and the micro- 

 phages. The macrophages or large phagocytes in- 

 clude the large lymphocytes, endothelial cells, 

 ameboid connective tissue cells and others which 

 may occasionally take up foreign particles. Our 

 polymorphonuclear leucocytes are the micro- 

 phages. In relation to immunity we are concerned 

 chiefly with the large lymphocytes (macrophages), 

 and the polymorphonuclear leucocytes (micro- 

 phages). Although such cells may contain many 

 ferments, Metchnikoff recognizes but one type in 

 relation to their resorptive, digestive and bacteri- 

 cidal activities. This he calls cytase and distin- 

 guishes that of the macrophage as macrocytase and 

 that of the microphage as microcytase. C} r tase 

 corresponds to the complement of Ehrlich. The 

 two cells do not have identical activities, the ma- 

 crophage being concerned specially in the resorp- 

 tion of tissue cells and in immunity to certain 

 chronic diseases, as tuberculosis and leprosy, 

 whereas the microphage is the cell which is con- 

 spicuously antimicrobic in relation to acute infec- 

 tions. 



of According to Metchnikoff, the leucocytes are 

 ' lls * very active in the resorption of useless or foreign 

 cells. During the metamorphosis of certain in- 

 vertebrates it is said that the larval tissues are 

 englobed and digested by wandering pha- 

 gocytic cells. In involution of the uterus 

 the muscular tissue is invaded by leuco- 

 cytes which take up and digest or carry away the 

 "retrogressive elements." MetchnikofFs concep- 

 tion of certain atrophic processes, particularly 



