CONDITIONS OF LIFE OF NITRIFYING ORGANISMS 67 
widely distributed, probably in all soils, and is able to convert 
any kind of nitrite into nitrate. It cannot, however, act upon 
any nitrogen compounds except nitrites, and hence its action 
must be preceded by that of the nitrite bacteria. 
Unless there are other still unknown nitrifying bacteria, it is 
evident that in ordinary soil these two kinds of nitrifiers act to- 
gether and simultaneously. So closely connected is their action 
that it is difficult to find any traces of nitrites in the soil, since 
they are converted into nitrates as rapidly as they are formed. 
The whole nitrification may be very rapid. If ammonium salts 
are added to soil, they cannot commonly be found in the drainage- 
water from the soil, since the nitrification progresses so rapidly 
that they become completely converted into nitrates before drain- 
ing away. But though occurring simultaneously, the two steps 
in the nitrification appear to be distinct and produced by distinct 
organisms. It has been suggested recently that there are other 
classes of soil organisms that take these two steps in one, convert- 
ing ammonia and possibly even organic matter directly into ni- 
trates. 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 stimu- 
lating 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 solu- 
