ANILINE DYES — LEIKIND 441 



the germs of leprosy (now called Hansen's disease) , cholera, typhoid 

 fever, puerperal fever, pneumonia, glanders, diphtheria, brucellosis, 

 malaria, tetanus, and others. 



The discovery of bacterial and parasitic causes of disease led at 

 once to attempts at prevention and cure. In the field of surgery 

 Joseph Lister worked out the principles of antisepsis, later modified 

 to asepsis. These were primarily techniques for keeping bacteria 

 away from a surgical operative field by the use of antiseptics and 

 sterilized instruments and dressings. Thus the horrors of wound 

 infection were removed from the operating room and hospital wards. 

 In this field also, coal-tar derivatives played a most important role 

 in serving as a source for antiseptic agents for wound dressings and 

 as a sterilizing medium for instruments. 



But the real impact of aniline dyes in the field of therapeutics was 

 made by the work of Paul Ehrlich, who was born in eastern Germany 

 in 1854, just two years before Perkin made the first coal-tar dye. 

 Like Perkin, Ehrlich was also a very young man when he made his 

 first notable scientific contribution. While still a medical student he 

 began to study the effect of dyes on tissues. Stimulated by the work 

 of his teacher Julius Cohnheim and his cousin Carl Weigert, Ehrlich 

 became interested in the chemistry of dyes and the relation of chemi- 

 cal structure to specific actions on cells. The coal-tar dyes very 

 quickly attracted his attention, and he was the first to recognize the 

 biological difference between acid and basic dyes. This led him 

 during the years 1877 to 1880 to his epochmaking studies on blood in 

 which he differentiated several varieties of white blood corpuscles 

 by means of their responses to stains. These included basophiles, 

 eosinophiles, neutrophiles, lymphocytes, and monocytes. He was the 

 first to recognize stippling in red blood cells and described the earliest 

 known case of aplastic anemia, Shortly after leaving medical school, 

 Ehrlich was invited by Robert Koch to work in his laboratory in the 

 Imperial Health Office in Berlin. He arrived there about the time 

 that Koch was carrying on his classic researches into the cause of 

 tuberculosis. On the day after Koch announced his discovery of 

 the tubercle bacillus, Ehrlich devised an improved method of stain- 

 ing the organism with aniline dyes. Ehrlich's method is still used in 

 every diagnostic laboratory, although it is known to generations of 

 technicians as the Ziehl-Nielson stain because of two minor technical 

 modifications introduced by these workers. Ehrlich also worked out 

 the rationale of the polychromatic staining methods which have since 

 become so popular and useful. There are numerous modifications 

 among which may be mentioned Unna's polychrome methylene blue, 

 Mallory's aniline blue connective tissue stain, Romanowsky's eosin 

 methylene blue stain for use on blood smears and for the diagnosis 



