264 Joumal of Agricultural Research voi. xxx, no. a 
the protein will liberate only a small 
amount of energy must be considered; 
the organism has to decompose the 
amino acids and other nitrogen deriva¬ 
tives of the protein molecule, and 
•different organisms may attack differ¬ 
ent amino acids with a different degree 
of rapidity. 
The amino compounds are therefore 
formed and decomposed; they will 
accumulate in the medium only if 
the particular organism is unable to 
use these compounds or the larger part 
of them, formed from the protein; 
they will disappear only when the 
organism attacks them as readily as 
it does the protein or when another 
organism is present that attacks these 
compounds as soon as they are formed 
by the other organism from the protein 
molecule. It would be expected that 
different organisms will not only differ 
in the rapidity and completeness with 
which they are able to hydrolyze one 
protein, and especially different pro¬ 
teins, but also in the kind of amino 
acids which they are able to utilize 
as sources of carbon and nitrogen. 
Taylor (#7), for example, found that 
Bacterium coli did not produce amino 
acids from casein, but Proteus vulgaris 
produced lysin and histidin. When an 
available carbohydrate is present in the 
medium, the organisms may prefer this 
as a source of energy and attack the 
protein only as a source of nitrogen; 
they may, however, prefer the protein 
to the carbohydrate also as a source 
of energy. This is the reason for the 
various discrepancies reported in the 
literature on the sparing action of 
carbohydrates. When the carbohy¬ 
drate is utilized in preference to the 
protein as a source of energy the latter 
is decomposed only to a limited extent, 
according to the nitrogen requirements 
of the organism; therefore the ammonia 
and perhaps even the amino nitrogen 
may not accumulate and may even di¬ 
minish. When the protein is preferred 
as a source of carbon to the available 
carbohydrate, the amino nitrogen and 
ammonia may accumulate. 
There is another possibility when 
an organism prefers only certain 
amino acids as sources of nitrogen, 
that it will decompose large quan¬ 
tities of protein to enable it to obtain 
the particular amino acids, leaving the 
others to accumulate in the medium. 
Thus the amount of amino nitrogen 
formed from the decomposition of 
proteins may fluctuate, indicating that 
it is continuously formed and decom¬ 
posed by the organisms, as shown 
by Sears {25 ); or steadily increasing 
concentrations may be obtained for 
strong proteolytic organisms, as in the 
case of Bacillus subtilis and B. pyocya - 
neus . Waksman {83) found that the 
bacterium B. coli gave an increase of 
amino nitrogen in plain broth while 
the fungus Aspergillus niger showed a 
steady decrease. DeBord (5) found 
that the presence of glucose in peptone 
media increases the rate of production 
of amino nitrogen in cultures of various 
bacteria. 
Use of ammonia as an index of de¬ 
composition of proteins and their deriv¬ 
atives by microorganisms .—One advan¬ 
tage of this method consists in the fact 
that ammonia is the end product of 
protein transformation and as such it 
is not transformed further by hetero- 
trophic microorganisms unless there is 
an available nonnitrogenous substance 
present as a source of energy. The 
great advantage of this method is that 
the largest part of the ammonia accu¬ 
mulates in the medium not as a result 
of the nitrogen metabolism of the or¬ 
ganism, but as a result of its carbon 
metabolism, when proteins and amino 
acids are used by microorganisms as 
sources of carbon, both as a source of en¬ 
ergy and for structural purposes; am¬ 
monia is then left as a waste product 
of respiration of the microorganisms. 
This is true for both bacteria and fungi 
and has been well recognized by the 
early bacteriologists, such as Marchal 
{17 ). The process of ammonia accumu¬ 
lation has been used most extensively 
in the literature of microbiology as an 
index of protein decomposition, espe¬ 
cially so in the branch of the subject ap¬ 
plied to soils, because of the difficulty of 
extracting and determining residual pro¬ 
teins or intermediary products in the soil 
as a medium, and the ease of ammonia 
determination. The term “ammonifi- 
cation” has come into general use, al¬ 
though the term ‘ ‘ ammonization ’ ’ 
would be the more proper one, since it 
came first into use in the nineties of last 
century, when suggested by Marchal. 
According to Butkevitch (5), am¬ 
monia formation is not the final stage 
in respiration, but the first stage, since 
ammonia is first split off (deaminized) 
from the amino acid, leaving the re¬ 
maining group available as a source of 
energy for the organism. 
Ammonia accumulation can serve as 
a good index of proteolysis only when 
no available carbohydrates are present; 
in the presence of the latter this - 
method should be supplemented by the 
study of another process, either the dis¬ 
appearance of original protein, or the 
formation of amino nitrogen. This 
accounts for the fact that Kendall anti 
Walker {12) y Butkevitsch {3), Marchal 
