PHAGOCYTOSIS 49 



and of digesting them; it is to these that Metchnikoff ascribed 

 the protective power of phagocytosis. Cells of a protecting 

 character in man are either microphages or macrophages. The 

 microphages are the polynuclear leucocytes, which are concerned 

 in the protection of the organism against acute infections, the 

 bacteria of which they take up and devour. The macrophages 

 consist of the large lymphocytes, the endothelial cells, and some 

 connective tissue cells, which take up foreign bodies. Both of 

 these classes contain ferments; microcytase being found in the 

 microphages; and macrocytase in the macrophages. The latter 

 absorb connective tissue cells through their particular ferments, 

 and are active in immunizing against tuberculosis. These cells 

 perform various functions in the body. When the tissues are 

 invaded with bacteria, the blood shows an increase in the number 

 of these microphages, which have been called the "hygienic 

 police." Summoned to repel invasion, they leave the lymph 

 stream for that of the blood. All the phenomena of leucocytic 

 emigration in inflammation is a manifestation of positive 

 chemo taxis. During practically all the infections, the peripheral 

 blood contains an excess of leucocytes over the normal amount 

 per cubic millimeter (7,600). In exceptional infections, typhoid 

 fever, influenza, measles, and tuberculosis, there is no such 

 increase, or leucocytosis. In malaria (not a bacterial infection) 

 there is also no leucocytosis. 



Metchnikoff has described a process in which the phagocytes 

 undergo what he calls phagolysis. The ferment, cytase, is dis- 

 charged and acts extracellularly, digesting the cell body and 

 freeing ferment which will act against the invaders. Metchnikoff 

 further claims that both phagocytosis and phagolysis, either 

 severally, or in combination, are responsible for natural or ac- 

 quired immunity. 



In the case of acquired immunity, it is supposed that the leuco- 

 cytes become educated. Regarding the toxins against which 

 animals can be immunized by gradually increased doses, it is held 



