20 JOURNAIv OF THE 



warm countries where the natives collect the nitrates 

 accumulated as an incrustation on the soil, they are 

 aware of the fact that the efficiency of the bed depends 

 on removing- only the upper crust. Waring^ton found 

 the following- amounts of Nitrog-en as nitrate in two 

 fallow soils at R jthamsted: 



In the fir.^t nine inches 25.5, 40.1 lbs. 

 •' "second " " 5. 0, 14.3 " 



•' " third " " 5.5. " 



Portions taken at different depths were added to di- 

 luted, sterilised solutions of urine containing- a little 

 calcium carbonate and gypsum. The formation of ni- 

 trates was accepted as evidence of the presence of the 

 org'anisms. In this way Warington succeeded in de- 

 tecting their presence at depths of six feet from the 

 surface, below this he was unable to find them. It is 

 especially note-worthy that there was always a period 

 of inactivity followed by a period of activity after the 

 introduction of the soil portions. This he regfarded as 

 due to incubation, and the time required was much less 

 in the case of surface portions. We would naturally 

 expect to find any forms of life near the surface, and 

 especially so, since the conditions most essential for 

 their growth exist in greater abundace in surface soils. 

 While Waring-ton's cultures were made in solutions, in 

 which the conditions were not the same as those of the 

 soil, he was better able to control them, emd to make 

 the experiments of any desirable composition. But lit- 

 tle is known of the way in which they iict, only certain 

 products are obtained as a result of the organisms' ex- 

 istence. AVhen a suitable nitrifiabie solution is seeded 

 with either a portion of a nitrified solution or of a soil 

 or soil infusion, nitrates are usually produced as the 

 final result. In some cases notable quantities of ni- 



