256 SCIENCE PROGRESS. 



by its complexity when we remember the extraordinary and 

 fruitful results that have been obtained already during the 

 last two or three decades. First came the recognition of the 

 fact that every fertile soil abounds in microscopic organisms, 

 and this to a startling degree. Taking at haphazard some 

 later enumerations as more reliable than the earlier ones, 

 Beumer (8) found 44,000,000 to 45,000,000 of germs of 

 various kinds in 1 c.c. of sandy humus ; Maggiora (9) 

 got 11,000,000 in the soil of fields ; and Caron (10) 

 gives up to 15,000,000, and so the numbers proceed. 



We may expect about 1,000,000 to 10,000,000 of germs 

 then in a small thimbleful of such soil. What are these germs 

 doing ? A few are undoubtedly those of injurious para- 

 sites ; others are merely the fungi and bacteria which live 

 as saprophytes on the decaying vegetable and animal 

 remains, and their study is bound up with the whole ques- 

 tion of the manure heap and the fermentations and putre- 

 factions which bring organic substances back again into the 

 forms of carbon-dioxide, water, and ammonia; yet others are 

 now known from the researches of Schloesing and Miintz 

 (11), Warington (12), Frankland (13), and especially Wino- 

 gradsky (14), which oxidise ammonia to nitrous and nitric 

 acids ; while yet others, as appears from works by Breal, 

 Heraeus, Frankland, Gayon and Dupetit, and especially 

 Giltay and Aberson, and Burri and Stutzer (15), undo the 

 work of these " nitrifying" bacteria, and "de-nitrify," as the 

 ill-chosen term has it, the highly oxidised salts of nitrogen, 

 that is de-oxidise nitrites to nitrates and ammonia, and 

 even to free nitrogen. 



In addition to these forms occupied in oxidising am- 

 monia and in reducing nitrates, however, the researches of 

 Berthelot (16) and Winogradsky (17) point to the existence 

 of forms which, provided there are plenty of carbo-hydrates 

 available, can fix free nitrogen in their living machinery, 

 and by means of energy obtained from the destruction of 

 relatively wasteful quantities of carbon, compel this nitro- 

 gen to enter into synthesis. In the case of Winogradsky's 

 work, and the known ability of the observer, it certainly 

 does look as if he had succeeded in isolating a definite 



