82 AGRICULTURAL BACTERIOLOGY. 



and those remaining lie in the soil ready to grow again when 

 more organic matter comes within their reach. By their action, 

 then, every bit of organic matter which reaches the soil is seized 

 and rapidly decomposed. 



The chemical nature of these destructive changes is very 

 complicated and highly varied. It will be a long time before 

 our chemists understand them, for they involve problems in 

 physiological and organic chemistry which are yet unsolved. 

 We know that as a result of the decompositions many new 

 products are formed, and that these new products must be re- 

 garded as belonging to at least two types, so far as concerns 

 their relation to the bacteria. Some of them must be regarded 

 as secretions or excretions from the bacteria and hence as the 

 result of the active metabolism of the microorganisms. These 

 are probably rather small in amount but of great significance 

 in some connections, inasmuch as many of them are especially 

 poisonous. Others must be looked upon as by-products of de- 

 composition. By this is meant that, as the bacteria take cer- 

 tain atoms from the complex molecules for their own use, the 

 rest of the molecule can no longer retain its earlier form, and 

 consequently its atoms must enter into new relations to form 

 new bodies. These by-products, of course, have never been 

 actually in the bacteria and are not the direct results of metabo- 

 lism. The new products formed in the decomposing mass are 

 partly gaseous. This is proved by the odor that commonly 

 arises from decaying bodies which are indications of the exha- 

 lation of volatile products. A chemical study has shown in 

 many cases the actual nature of these gaseous products, indi- 

 cating them to be chiefly CO 2 , H, CH 4 , NH 3 , H 2 S and N, in 

 addition to others, present in much smaller amount, producing 

 the peculiar and characteristic odors. Some of the new prod- 

 ucts are solids and may be either soluble or insoluble. If 

 soluble they are sure to be dissolved in the course of time by 

 the water which falls upon the decaying mass and, in solution, 



