TRANSFORMATIONS OF CARBOX AND NITROGEN. 95 



shows that the soil must contain the nitrifying organisms. 

 But the bacteria which were found in such soil by ordinary 

 methods showed no power of nitrification. Evidently the 

 reason was that the nitrifying bacteria did not make themselves 

 evident with the ordinary bacteriological methods. 



The cause of the trouble and the secret of successful study 

 was soon learned by a Russian naturalist, Winogradsky (1890). 

 In bacteriological studies the common method of isolating 

 bacteria is to get them to grow in certain definite culture 

 media made by the bacteriologist. Such media, as commonly 

 used, contain a certain amount of organic compounds which 

 serve as food for the bacteria. Winogradsky proved that in 

 such media the nitrifying bacteria will not grow. The pres- 

 ence of a small amount of organic matter in the culture media 

 is directly injurious to these organisms, and the media which 

 support ordinary bacteria luxuriantly will not allow the nitri- 

 fying bacteria to grow. Having reached this conclusion Wi- 

 nogradsky, by a series of very ingenious experiments, was 

 finally successful in isolating from the soil an organism, which 

 proved to be a definite species of bacterium, and which was 

 able, under proper conditions, to carry on this oxidation of ni- 

 trites and ammonia in such a way as to result in the produc- 

 tion of nitrates. 



While the original discovery belongs to Winogradsky it 

 must be mentioned that precisely similar results were obtained 

 almost simultaneously, and quite independently, by two Amer- 

 ican bacteriologists (Jordan and Richards). As soon as these 

 discoveries were announced others followed rapidly along the 

 path pointed out, so that in a short time the results were 

 thoroughly verified and demonstrated. 



For a while the results of experiments were in some con- 

 fusion since in some cases nitrates appeared to be formed while 

 in others they did not. It became evident that nitrification 

 was not a simple phenomenon. It was Winogradsky again, who 



