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 
