HUMUS 69 



humus, on the other hand, is acid in reaction. The 

 conditions under which it has been formed have 

 largely checked the growth of bacteria, and result in 

 putrefaction rather than in decay. Whereas in the 

 former the organic material liberates Carbon dioxide 

 in quantity is decomposed in fact by slow com- 

 bustion the latter, acted on in the absence of air, 

 takes the Oxygen it needs for the oxidation of its 

 Carbon from the organic substance itself, and 

 eliminates also from the mass such gases as marsh 

 gas (CH 4 ) . It is for this reason that the end-products 

 in the two cases are different. In mild humus 

 organic bodies are formed from which the Nitrogen- 

 fixing bacteria can derive their energy and food, and 

 on which, too, the plants can feed directly. In raw 

 humus the end-products are a mixture of com- 

 pounds known as Humic acid, or Humin, that 

 prevent the growth of bacteria, that are in fact anti- 

 septic, and that do not furnish the plants with food 

 material in a form in which they can assimilate it. 

 Peat, in fact, is raw humus. It not only fails to 

 undergo decomposition while remaining in the 

 swamp, but when put on the land in its raw state it 

 undergoes decomposition very slowly, and definitely 

 retards the growth of crops. It is only necessary 

 to contrast peat with the humus that can be 

 seen as a rich, dark liquid oozing out of a manure- 

 heap to realize the difference between the humus 

 rich in the substances required for plant food, 

 and that in which available food substances are 

 wanting. 



In stating that great progress may be looked for 



