METCHNIKOFF 265 



other diseases. In Germany, Robert Koch, after 

 discovering the bacillus of tuberculosis, confirmed 

 and extended the work of Pasteur on anthrax. 

 Koch or his disciples discovered the cause of 

 cholera, enteric fever, lock-jaw, dipththeria, glan- 

 ders, etc. Pasteur made discoveries of fundamen- 

 tal importance in relation to hydrophobia and its 

 treatment which have resulted in the saving of 

 innumerable lives. Whilst omitting minor dis- 

 coveries we may add that Bruce, working in 

 Malta, discovered the cause of undulant fever. 



Meanwhile the eminent Russian zoologist Metch- 

 nikoff, when studying small fresh-water Crustacea 

 known as Daphnia, observed that they were para- 

 sitized by microorganisms which were frequently en- 

 gulfed by the wandering cells in their body cavities. 

 He next studied the behaviour of anthrax bacilli in 

 the body of the frog, an animal which under ordinary 

 conditions is resistant to infection with this micro- 

 organism. He observed that the bacilli soon after 

 their introduction beneath the animal's skin were 

 taken up by the frog's wandering cells or leuco- 

 cytes after which they degenerated and died. 

 Metchnikoff next advanced a fascinating explana- 

 tion of these phenomena. He regarded the wan- 

 dering cell in the animal economy as a cell having 

 varied functions, amongst others that of defending 

 the body against invasion by the germs of disease. 

 He drew a graphic picture of the wandering cells 

 (to which he gave the name of phagocytes) seizing 



