1893.] Bacteriology in its General Relations. 855 
had separated from the soil. Warington states, that over a 
hundred different species of bacteria had each been carefully 
tested as to their ability to nitrify ammoniacal solutions and 
that with every one a negative result was reached. It is less 
than three years ago that the efforts of bacteriologists to 
obtain the specific cause of the process were crowned with 
success. Frankland isolated the germ by dilution, and at the 
same time Winogradsky succeeded in separating it by another 
process. The unique feature of this germ was that they could 
not make it grow upon gelatine. This peculiar individuality 
explained the failure of previous investigators who had con- 
fined their methods to gelatine media. Experiments demon- 
strated that this germ was only able to oxidize ammonia into 
nitrous acid: Important as was this discovery, it was only 
one step in the process. The conversion of nitrous acid and 
its salts into the more stable nitrates, eluded their best efforts. 
Winogradsky at last succeeded in isolating the organism 
from mixed cultures by the use of gelatinous silica mixed 
with inorganic salts. 
In this way the various steps of the process were clearly 
demonstrated and the biological theory of nitrification was 
established upon a firm and scientific basis. This theory 
claims that the nitrification of ammonia in the soil takes 
place in two. successive stages, the change in each case being 
produced by distinct and separate organisms. In the first 
stage ammonia is oxidized into nitrous acid and then this is 
acted upon by another (a second) organism and is converted 
into a nitrate. Ordinarily, as observed in nature, the two pro- 
cesses occur simultaneously so that the ammonia passes in 
continueus combination from its simpler form into its ultimate 
stage as nitric acid, or some of its salts. The economic value 
of this discovery cannot be estimated. It is not only a com- 
plete and satisfactory scientific solution of a complex process, 
but is of invaluable aid to the agriculturist in demonstrating 
to him the source of the most essential element in soil restora- 
tion and in teaching him how he can best conserve and 
utilize this expensive product. 
It has also an important bearing upon certain phases of 
