440 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1957 



disease of cattle. He saw the germs of the disease in the blood of 

 infected cattle. He was able to grow these germs outside the animal 

 body for several generations in culture media which he devised ; and 

 when he reintroduced these germs into susceptible mice they promptly 

 became ill and died of anthrax infection. 



While Koch was carrying on these investigations, another worker, 

 Carl Weigert, was working along a line that converged on Koch's 

 problem. Weigert as a pathologist was concerned with methods of 

 recognizing cellular elements under the microscope. He knew about 

 the new dyes that were appearing from the great chemical factories 

 in Germany. He was also aware of one of the cardinal problems in 

 the infant science of bacteriology. This was the question of recogniz- 

 ing the presence of bacteria in tissues. In the unstained state they 

 were almost impossible to distinguish from other cellular structures. 

 Weigert tested a number of dyes, and in 1875 he was successful in 

 demonstrating cocci in tissues by the use of methyl violet, a coal-tar 

 stain. In 1877 he successfully stained anthrax bacilli in various 

 organs of a dog using methyl violet, Bismarck brown, and other 

 aniline colors. These results helped enormously in convincing skep- 

 tics that there might be something to the germ theory of disease. 



Robert Koch now began to perfect methods for handling and 

 observing bacteria, techniques without which bacteriology could not 

 emerge as a science. He developed the solid-culture method for 

 isolating and growing pure cultures of bacteria. Then he devised a 

 simple method for staining bacteria outside the body tissues. In the 

 living state, especially while in motion, microbes were almost im- 

 possible to resolve and identify under the microscope. This fact 

 made accurate diagnosis practically hopeless, and study extremely 

 difficult. Koch solved the problem by making very thin smears or 

 films of bacteria from cultures, body fluids, or exudates on glass 

 slides or cover slips. These films were fixed by gentle heat or air 

 drying and were then stained. The organisms now stood out sharp 

 and clear in a microscopic field without distortion or alteration of 

 size. Koch found that of all dyes the aniline colors were best suited 

 to bacteriological work. He further found that such stained prep- 

 arations could easily be photographed. From his photographs, 

 Koch was able to confirm the existence of flagellae in bacteria, struc- 

 tures about which a controversy had been raging between those who 

 claimed they saw them and those who said they were imaginary. 

 Within a span of about two decades, often called the golden age of 

 bacteriology (1875-95), with the aid of pure culture techniques and 

 staining methods devised by Koch and his school, the causative 

 agents of many of the most important diseases afflicting man and 

 animals were identified. These included the tubercle bacillus and 



