HISTORICAL AND INTRODUCTORY 23 



position there taking place was not the purely chemical 

 " eremacausis " Liebig had postulated. Pasteur himself had 

 expressed the opinion that nitrification was a bacterial pro- 

 cess. The new knowledge was first brought to bear on 

 agricultural problems by Schloesing and Muntz (245) in 1877 

 during a study of the purification of sewage water by land 

 filters. A continuous stream of sewage was allowed to trickle 

 down a column of sand and limestone so slowly that it took 

 eight days to pass. For the first twenty days the ammonia 

 in the sewage was not affected, then it began to be converted 

 into nitrate ; finally all. the ammonia was converted during its 

 passage through the column, and nitrates alone were found in 

 the issuing liquid. Why, asked the authors, was there a 

 delay of twenty days before nitrification began ? If the pro- 

 cess were simply chemical, oxidation should begin at once. 

 They therefore examined the possibility of bacterial action 

 and found that the process was entirely stopped by a little 

 chloroform vapour, but could be started again after the 

 chloroform was removed by adding a little turbid extract of 

 dry soil. Nitrification was thus shown to be due to micro- 

 organisms " organised ferments," to use their own expression. 



Warington (295-6) had been investigating the nitrates in 

 the Rothamsted soils, and at once applied the new discovery 

 to soil processes. He showed that nitrification in the soil is 

 stopped by chloroform and carbon- disulphide ; further, that 

 solutions of ammonium salts could be nitrified by adding a 

 trace of soil. By a careful series of experiments described in 

 his four papers to the Chemical Society he found that there 

 were two stages in the process and two distinct organisms : 

 the ammonia was first converted into nitrite and then to 

 nitrate. But he failed altogether to obtain the organisms, in 

 spite of some years of study, by the gelatin plate methods then 

 in vogue. The reason was discovered later : the organisms 

 will not grow in presence of nitrogenous- organic matter. 

 Not till 1890 did Winogradsky (311) succeed in isolating 

 them, and thus complete the evidence. 



Warington established definitely the fact that nitrogen 



