FIXATION OF NITROGEN 49 



in which they were growing was found to become 

 richer and richer in nitrogen compounds. 



To the chemist these results were a mystery, and 

 it was not until a fresh method of attack was devised 

 that the truth emerged. 



While Liebig, Lawes, Gilbert, and others, were dis- 

 cussing agricultural problems purely from the 

 chemical standpoint, Pasteur had begun to show the 

 paramount importance of bacteria. It was estab- 

 lished by him that putrefaction and decomposition 

 were brought about by the action of bacteria, and 

 the successes he had obtained in combating terribly 

 serious plant diseases in France had been so sen- 

 sational as to attract those interested in agriculture 

 to the importance of bacteria. It seemed possible 

 that bacteria might be closely connected with the 

 changes going on in the soil. 



The first of a series of classical experiments was 

 published in 1877. In that year Schloesing and 

 Miintz allowed some sewage water to trickle very 

 slowly through a filter of sand and limestone. During 

 the first twenty days of the experiment the Ammonia 

 in the sewage passed unchanged. Then it was 

 noticed that some of it was changed into nitrate, and 

 after a short time it was found that all the Ammonia 

 which went in at one end of the filter .was changed 

 to nitrate, and emerged at the other end of the filter 

 in the form of nitrate. If the phenomenon had been 

 purely a chemical one, there was a mystery as to why 

 the filter should be inactive for the first twenty days ; 

 but if it was connected with the growth of living 

 organisms, it was natural that time would have to 



4 



