ROBERT KOCH 9 



He had learned how to isolate and cultivate bacteria, and how to study their 

 effect on animals ; but with the minutiae of their morphology or physiology, 

 apart from any significance these might have for the problem in hand, he was 

 not greatly concerned. Duclaux relates that a clever and positive microscopist, 

 who told Pasteur in very cautious language that a certain organism which 

 he had taken for a coccus was in reality a very small bacillus, was much aston- 

 ished to hear him reply : " If you only knew how little difference that makes 

 to me ! " 



One further point must be noted. Pasteur and his colleagues had shown how 

 to obtain cultures of micro-organisms, and propagate them indefinitely in the 



Fig. 2.— Robert Koch (1843-1910). 



laboratory ; but the methods which they employed were not well suited to the 

 isolation of pure strains of bacteria from an originally mixed culture, except in 

 those relatively rare cases in which it was possible to employ a highly selective 

 medium. Since all media were employed in the fluid state, the only method of 

 purifying a culture was to make successive transfers with very small amounts of 

 material, in the hope that only a few bacteria, all of one kind, would be carried 

 over. Such a technique was very uncertain in its results. 



Pasteur, starting as a chemist, founded bacteriology and revolutionized medi- 

 cine. At about the time when he was propounding his germ theory of disease, 

 a young German physician, some twenty years his junior, was turning from 

 clinical medicine to bacteriology. Kobert Koch (1843-1910), at that time a 



