CONDITIONS OF LIFE OF NITRIFYING ORGANISMS. 6l 



though occurring simultaneously, the two steps in the nitrification 

 appear to be distinct and produced by distinct organisms. It 

 has been claimed recently that there are other classes of soil organisms 

 that take these two steps in one, converting ammonia and even 

 organic matter directly into nitrates. If this be true, they represent 

 distinct classes of nitrifiers, but the observations have not yet been 

 sufficiently verified. 



CONDITIONS OF LIFE OF NITRIFYING 

 ORGANISMS. 



The importance of the phenomenon of nitrification makes it 

 very desirable to understand thoroughly the conditions under which 

 it may best occur, and, consequently, the means for stimulating 

 or hindering it. The conditions regulating the life of these nitrifiers 

 are, in some respects, peculiar. 



Organic Food. In respect to food these nitrifiers are among 

 the most remarkable of all organisms. Not only do they need no 

 organic food, but the presence of organic matter in the solutions, even 

 in small quantity, is directly injurious. The bacteria will grow 

 readily in mineral solutions, but if a small quantity of organic 

 matter is added, the growth stops. In ordinary laboratory solutions 

 a very small amount of organic matter acts like an antiseptic. In 

 the soil, however, the nitrifiers behave differently, and are not 

 checked in their growth by such small quantities of organic matter 

 as serve to check them in laboratory solutions. This injurious 

 action of organic matter is a curious phenomenon. The more 

 highly organized the compound, the more decided its checking 

 action, and thus, the more valuable the material for ordinary kinds 

 of bacteria, the greater its injury upon the nitric bacteria. These 

 bacteria thus grow under conditions detrimental to other bacteria, 

 but will not grow under the conditions which other species find 

 most favorable. A more sharp contrast can hardly be conceived. 

 Not only bacteria, but all other colorless plants are obliged to depend 

 upon organic food as a source of energy, in this respect resembling 

 animals. But here is a group of organisms that not only does not 



