Aug. 3, 1908.] AgiHcuUural Gazette of N.S.W. 659 



and allied forms of micro-organisms, terrible as they manifest themselves at 

 times, are numerically insignificant in comparison with the great number 

 which may be termed either directly or indirectly beneficial to the higher 

 forms of life, and still more with those which are decidedly harmless, and whose 

 role in the economy of nature is not understood at present. Many hundreds are 

 well known, and their characteristics have been worked out, and as researches 

 progress they are constantly added to. Being of very delicate structure they 

 are very sensitive to external conditions, especially to the presence or absence 

 of oxygen, which striking characteristic divides them into two distinct groups. 

 Those which require oxygen for their growth, and prosper ill without it, are 

 called aerobic, and those upon which oxygen has a toxic efEect, are called 

 anaerobic bacteria. 



Nitrogen. 



In order to fully understand the importance of the bacteria to be specially 

 discussed, it is necessary to make a few remarks regarding the element 

 nitrogen, which is absolutely needed as a food by all animated nature. 



Nitrogen in its simple form is a gas abundantly present in our atmosphere, 

 where it is practically inert, and acts as a diluent of oxygen, the element 

 required by all breathing beings. In this simple form it is otherwise perfectly 

 useless to either plants or animals. Moreover in this state it will not readily 

 combine even with oxygen, almost the only element it attaches itself to when 

 in the elementary state. Plants, however, cannot utilise it unless it has 

 been oxidised into nitric acid. In that form only is it assimilable by plants 

 which possess the power of elaborating it into other complex compounds known 

 by the term of organic-nitrogen compounds, and albuminoids, in which forms 

 it serves as food for animals. The fact must not be lost sight of —that whilst 

 animals require organic nitrogen compounds for their nutrition, plants cannot 

 directly utiUse again the compounds they elaborate, but require them sim- 

 plified into nitric acid. This is done by bacteria, a group of which are called, 



Nitrifying Bacteria. 

 As soon as a plant or animal is dead it is attacked by bacteria whose function 

 it is to reduce it into the elements from which it was built. The same appUes 

 to any dead organic substance, the voidings of animals, offal of any kind, 

 stable manure, &c. These bacteria are the putrifying organisms, of which 

 there are a number of forms, and which are the forerunners of the nitrifying 

 bacteria. In the process of decay different gases are evolved during the 

 progress of fermentation. Some bacteria liberate nitrogen, and others am- 

 monia, from the organic nitrogenous compounds. The nitrogen so evolved 

 is lost in the air, but the ammonia, unless the fermentation is very violent, 

 and the bacteria cannot consume it, is fastened on to by a certain type of 

 organism and converted by it into nitrous acid. This is the first stage of 

 nitrification, the organisms bringing the ammonia to a lower state of oxidation 

 than that required by the higher plants. The further oxidation^ of ^nitrous 



