CHAPTER VI 



HUMUS 



Humus as the home of bacteria Soil composed of mineral 

 debris and humus Influence of mineral debris secondary 

 Bacteria and plants and animals The sun and food as pro- 

 ducers of energy Humus as a source of energy Life 

 limited by the food-supply Mild humus and raw humus 

 Their properties Bacteria as chemical agents Complexity 

 of humus Four groups of compounds Only one carbo- 

 hydrate isolated from humus Carbohydrates and humic 

 bodies Effect of boiling carbohydrates with hydrochloric 

 acid Humic acid formed before humin Difference between 

 natural and artificial humic acid The difference reconciled 

 No real formula for humic acid Effect of boiling carbo- 

 hydrates with organic acids Effect of heating carbo- 

 hydrates Nature of humic bodies obtained Proteins and 

 humic bodies Nature of changes in formation of peat 

 Causes of complexity of humic bodies. 



EMPHASIS has been laid in the previous chapters on 

 the fact that the attention of all growers, directed 

 until recently on to the chemical and mechanical 

 aspects of the soil, has during the last few years been 

 focussed chiefly on the soil as the seat of changes 

 brought about by the bacteria that inhabit it. In 

 the last chapter, dealing with the fixation of nitrogen 

 from the soil air by leguminous plants, it was neces- 

 sary to refer briefly to the fixation of nitrogen by 

 bacteria which have no relation with leguminous 

 plants. These will have to be considered at length 



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