50 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS. 



and small, secrete it or an allied substance, and the total is enor- 

 mous. What becomes of it all? 



Thus the nitrogen of the nitrate absorbed by the plant has 

 reached two quite different conditions. Part of it is still in the 

 highly complex form of proteid, either in the dead body of the 

 animal or the plant. A second part has been partly broken down 

 in its passage through the animal's body, and has reached the con- 

 dition of urea or some allied body. But in neither condition is it 

 within reach of another generation of green plants. It must be 

 still further broken down before it is available for plants. 



ORGANIC NITROGEN. ITS DECOMPOSITION. 



Decomposition in General. This means the breaking to 

 pieces of complex compounds so as to form simpler ones. The 

 term thus denned is a very broad one, and covers a long series of 

 changes, of a purely chemical nature. But more commonly the 

 term has a narrower meaning, and refers to the breaking down of 

 organic products under the influence of microorganisms. This is 

 one of the most important functions of soil bacteria. The destruc- 

 tion of nitrogenous compounds, urea proteids, gelatins, or other 

 bodies, is brought about by several agencies, but the chief one is 

 undoubtedly that of microorganisms. A small amount of the pro- 

 teid appears to be decomposed in plant tissue without the aid of 

 bacteria; another portion is broken down by yeasts; another by 

 molds and other fungi. But decomposition is chiefly due to a class 

 of bacteria called the decomposition bacteria. 



But even as thus limited, this term is still a broad one including 

 different species of bacteria and various types of decomposition. 

 Two types are generally recognized, under the names of decay 

 and putrefaction. These two terms are frequently not very clearly 

 distinguished, being used indiscriminately to refer to the decomposi- 

 tion of organic substances under the influence of bacteria. There 

 is a distinction between them, however, which may be properly 

 drawn. 



Putrefaction. This is the name given to a partial decomposi- 



