70 THE SPIRIT OF THE SOIL 



in agriculture as a result of emphasizing the import- 

 ance of bacteria instead of restricting the outlook to 

 the chemical composition of the soil, it has to be 

 realized that from one very important point of view 

 agriculture must always be regarded as a purely 

 chemical process. It will always be possible to 

 express what happens when a crop has grown from 

 seed to mature plant, by an analysis of the completed 

 plant on the one hand and an estimate of substances 

 taken from the air and the soil on the other. So 

 long as the botanist or agriculturist bears in mind 

 that, in so doing he has not expressed the full process 

 it is as desirable to-day as ever it was that all 

 information possible should be derived from the 

 chemical conditions underlying growth. While it 

 is correct to state that one of the most important 

 properties of the humus is its power of enabling 

 the bacteria to develop in the soil, it is also well 

 to bear in mind that the value of the bacteria so 

 growing in the soil lies in the products of their 

 activities, which are essential for satisfactory plant 

 growth. 



Humus, when one starts to consider it from the 

 chemical standpoint, is a highly complex mixture of 

 various compounds, which it has hitherto proved 

 impossible for the chemist either to separate or 

 satisfactorily to analyze. For very many years it 

 has formed the subject of keen interest and dis- 

 cussion. Naturally enough, perhaps, in early days 

 it was regarded as being of very simple composition. 

 De Saussure, for instance, in 1804 described it as a 

 ' ' brown combustible powder soluble in Alkalies and 



