AGRICULTURAL EXPERIMENTS 249 



few illustrations of the further developments that have come 

 to light may be given here. 



When the Rothamsted experiments were begun, nothing 

 was known as to how such processes as fermentation and 

 decay took place. Liebig and others had attempted certain 

 explanations but that the actions were carried on by living 

 organisms was entirely unsuspected. With the development 

 of knowledge of the actions of the yeast plant in producing 

 alcohol and the early studies of bacterial change carried 

 out by Pasteur, attention began to be directed to the soil 

 as a possible seat of similar actions. In particular it had 

 always been recognised that soil is capable of transforming 

 almost any form of organic compound of nitrogen into nitrates. 

 The higher plants, for example, can only take in nitrogen 

 as nitrate and yet it is a matter of indifference whether we 

 supply a crop growing in ordinary soil with nitrogen as 

 nitrate, ammonia or the various forms present in such material 

 as farmyard manure. Clearly some processes must be at work 

 in the soil transforming these compounds into nitrates. This 

 has proved to be the case. In 1877 Schloesing and Miintz 

 were able to demonstrate that the change was a vital one, 

 as it is suspended when the soil is saturated with chloroform 

 or other antiseptics which will put living organisms out of 

 action by killing them. 



The late Robert Warington was then working in the 

 Rothamsted Laboratory and immediately attacked the question 

 in the light of Schloesing and Muntz's announcement. After 

 confirming their results, he succeeded in showing that the 

 action must take place in two stages, each brought about by 

 different organisms, one of which transforms ammonia into 

 nitrite whilst the other completes the oxidation into nitrate. 

 Warington attempted the separation and isolation in the pure 

 stage of the two organisms but used the long and tedious 

 method of dilution and before he had succeeded in purifying 

 his cultures to the extent that would satisfy himself Wino- 

 gradsky published his very elegant method of isolation, which 

 depended upon the growth of the organisms upon a non-organic 

 solid medium — silica jelly. Warington's investigations on the 

 processes of nitrification were not confined to the laboratory. 

 He showed that the organisms are almost confined to the 

 surface layers of cultivated soils and his demonstration of the 



