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he said. " The small amount of it which you introduce into the soil 

 with your stable manure is nothing in comparison to what the soil 

 already contains of it. Mind the mineral salts which you take away 

 with each crop and return them to the soil." And yet the farmer's ex- 

 perience and scientific experiments alike stood against Liebig. No 

 amount of phosphates, or lime, or ashes, could produce, even in a soil 

 already rich in nitrogen, the effects produced by stable manure. The 

 latter gave vigour to the plants and seemed to vivify those very nitro- 

 gen compounds which already were stored in the soil. There the debate 

 stood when light was thrown upon it from a quite unexpected quarter. 

 Phenomena of life found their explanation in life, not in chemistry. 



The fascinating achievements of chemistry during the first half of 

 our century had created the tendency to explain all phenomena of life 

 by such simple chemical re-actions as we perform in our laboratories. 

 Animals and plants were treated like simple glass balloons, in which 

 any reaction may be provoked by adding some acid or some alkali. 

 However the old teachings of Leeuwenhoek and Cagniard Latour have 

 not been totally lost. Schwann — the father of the cell theory — was al- 

 ready reconstituting life to its real importance ; and when Pasteur 

 came forward with his epoch-making res arches into the chemistry of 

 the micro-organisms, he found science already prepared to accept his 

 teachings. At the present time, we know that no animal or plant, with 

 the exception of the lowest unicellular beings, can be considered as one 

 being — that each of them is a colony of multitudes of micro-organisms ; 

 and while we are more and more persuaded that chemical processes 

 which are going on within complex and unstable compounds are the 

 real basis of life, we know that the seat of these processes must be 

 looked for in the infinitesimal component parts of the organism and the 

 microscopical inhabitants of its organs. The study of these unseen 

 beings and of the chemical processes due to their activity has already 

 given the clue to many a scientific problem, and it also has finally 

 shown the way out of the above-mentioned contradictions. 



It is a well known fact that, if a field has been left uncultivated the 

 percentage of nitrogen in the soil goes on increasing, and even becomes 

 greater than it was in the very plants which have grown upon the soi 

 It has now been demonstrated by Mayer, Post, and Kostycheff that the. 

 increase is due to the lower fungi and micro-organisms which develop 

 in prodigious quantities in decaying vegetable matter. They live in it 

 and as they eliminate carbonic acid they increase the percentage of ni- 

 trogen in the vegetable mould. To their activities we are indebted for 

 the considerable amounts of nitrogen stored in the superficial layers of 

 the earth, and until lately man has been chiefly living upon the trea- 

 suries accumulated by the invisible workers. 



However, the nitrogen of the soil is of no direct avail for the plant if 

 it is in the shape of such organic compounds as are bound within the 

 vegetable mould. Plants cannot assimilate them. Nor is it available 

 if it is in the shape of those insoluble ammoniacal salts which are easily 

 formed in a clayey soil, The best case for the plant is when it appears 

 in the shape of nitric acid (a compound of one atom of nitrogen with 

 one of hydrogen and two of oxygen) or of nitrates — that is, of salts of 

 this acid. But nitric acid is only formed with great difficulty in the 



