8 Historical 



with determination of the size and shape of bacteria, and with at- 

 tempts at rudimentary classification. The activities of the organisms 

 and their role in natural processes either were not mentioned at all 

 or were merely a subject for speculation, although the important rela- 

 tion of the lower organisms to the higher forms of life, namely, 

 plants and animals, was gradually established. 



It is sufficient to refer in this connection to the detailed knowledge 

 that existed concerning the production of nitrates in soils and in 



Fig. 4. G. J. Mulder investigated in detail the chemistry of soil organic matter, 

 or humus, and its role in soil fertility. 



composts. When, after the Revolution, the French Republic found 

 itself blockaded by the English Navy and deprived of the possibility 

 of importing nitrate from India, instructions were given to French 

 farmers to accumulate nitrate by the proper composting of their 

 stable manure. These instructions were so clear cut, and the bio- 

 logical processes involved so well understood, that it is obvious that 

 nearly a century before the nitrate-forming bacteria were isolated 

 their activities and importance were well appreciated. 



By the middle of the last century, it was definitely established 

 that stable manure becomes a nutrient to plants only after it has 

 undergone a period of decomposition, or "fermentation," although 

 the exact nature of this process was hardly understood. The pro- 

 duction of ammonia and the liberation of heat, which are now recog- 

 nized to be the important phases of protein decomposition and of 



