32 BULLETIN 182, U. S. DEPARTMENT OF AGRICULTURE. 
of nitrate to nitrite in peptone broth was probably due to the fact, 
which has been previously explained, that the organisms of the 
group did not develop well in peptone solution. While they could 
use it as a source of nitrogen with a suitable source of carbon, it 
was a poor source of nitrogen when used alone. With beef extract 
a source of carbon was probably supplied for the alkali-forming 
bacteria from the salts of the organic acid present in the ex- 
tract; consequently these bacteria could grow better, and as a 
result there was a larger number of cultures which could reduce the 
nitrate to nitrite. 
It has been seen, however, that these bacteria could utilize nitrogen 
from nitrate; consequently it should be expected that all the cultures 
should show a reduction and a positive nitrite test. Tests were 
made, therefore, in a medium containing 0.2 per cent of sodium 
nitrate, 0.25 per cent sodium lactate, and 0.1 per cent sodium- 
dibasic phosphate in distilled water. This medium was inoculated 
and incubated at 30° C. for 14 days and then tested for the presence 
of nitrite. Table 14 shows that 57 cultures gave a positive nitrite 
test. Seven did not grow in the experiment, although at other 
times they grew in the same medium. The remaining four cultures 
did not show a positive nitrite test. In order to show that there 
was a growth in all cases except the seven mentioned, titrations 
were made to determine the production of alkaline carbonates due 
to the oxidation of the sodium lactate. It will be seen from the 
table that all the cultures except those which did not show any 
growth produced an alkaline reaction. Even the five cultures 
which showed negative nitrite tests produced an alkaline reaction, 
showing that the nitrogen for growth must have been obtained 
from sodium nitrate ; consequently there must have been a reduction. 
The probable reason why there was growth without a nitrite reaction 
is because nitrites may be utilized by this group of alkali-forming 
bacteria as well as nitrates. This is shown in Table 14 through the 
alkaline change in reaction in the medium composed of 0.2 per cent 
sodium nitrite, 0.25 per cent sodium lactate, and 0.1 per cent dibasic- 
sodium phosphate and distilled water. 
It will be seen from the results that all but 5 cultures produced an 
alkaline change, showing the ability of the organisms to utilize sodium 
nitrite as a source of nitrogen and consequently reduce it. The five 
cultures that failed to show the nitrite test in the sodium-nitrate 
medium all produced an alkaline change in the sodium-nitrite-lactate 
medium. It is probable that these organisms failed to show a 
positive nitrite test because the nitrite was used up as soon as formed 
from the nitrate. Since these alkali-forming bacteria could reduce 
nitrite, it was natural to expect that it might be possible to determine 
the reaction bv means of the determination of ammonia as shown by 
