IMMUNITY. 359 



and noted that after a very short time, the 

 germs had entirely disappeared. The eminent 

 naturalist Metschnikoff , has since urged with 

 great vigor the view that the wandering cells 

 of the body, known as the white blood-cells or 

 pus corpuscles, betake themselves to the place 

 threatened by the bacteria, where, acting as 

 l( devouring cells " or phagocytes, they engulf 

 the foreign bacteria, kill and digest them and 

 thus render them incapable of doing harm. 

 Certain of the fixed tissue cells, it is supposed, 

 also possess this power of phagocytosis. It 

 was known, some time ago, that the wander- 

 ing cells possessed the power of taking up into 

 themselves lifeless foreign elements found in 

 the blood and of removing them from the body- 

 fluids, thereby making and keeping the blood 

 and lymph channels free of foreign particles. 

 There arose, consequently, the question as to 

 whether the wandering cells generally kill the 

 living bacteria or whether perhaps other in- 

 fluences kill the bacteria, and the wandering 

 cells merely remove the lifeless bodies, just as 

 they would remove other foreign bodies for 

 the purpose of keeping free the circulatory 

 channels. (See frontispiece.) 



In 1884, Grohmann found that cell-free blood 

 destroyed moulds and bacteria. This fact was 

 observed afresh by Fodor, in 1887, and has 



