BANISHING THE PLAGUES 



function of the white blood corpuscles is to act as a 

 scavenger in the blood, attacking and devouring the 

 noxious germs that find entrance to the body. Ehr- 

 lich showed that it is particular tribes of the leuco- 

 cytes, more especially the ones which came to be 

 known as polymorphs (polynuclear leucocytes) that 

 make up the company of germ-fighters, which Metch- 

 nikoff had christened phagocytes or cell-eaters. 

 Another and smaller type of leucocyte Ehrlich chris- 

 tened the eosinophile (lover of eosin) because of the 

 readiness with which it absorbs the eosin stain. 



The functions of the less numerous tribes of leuco- 

 cytes have not been very clearly made out; but their 

 discovery was a step in the revelation of the com- 

 plexity of the blood which has been supplemented, 

 on the physiological side, by the studies in immuni- 

 zation, and by such remarkable demonstrations as 

 Professor G. H. F. Nuttall's tests through which the 

 genetic relationship of different animals may be 

 shown by examining a few drops of blood serum. 



THE SIDE-CHAIN THEORY 



Notwithstanding his successes in the anatomical 

 investigations, Professor Ehrlich's interests have all 

 along centered on the physiological and chemical 

 aspects of the problems of medical science. He made 

 very notable contributions to the theory of the new 

 science of immunity not long after the investigations 

 of Von Behring gave the diphtheria antitoxin to the 

 world. Ehrlich experimented with certain vegetable 

 products, notably ricin, a derivative of the castor oil 

 bean. His line of research had to do with rendering 



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