Journal of Agricultural Research 
Vol. VIII, No. 3 
114 
Ammonia production. —Cultures in Dunham’s peptone solution were 
tested at the end of one, two, three, and four days as follows: In clean 
test tubes of the same internal diameter there were placed 10 c. c. of 
ammonia-free water. Into each was placed one 2-mm. loopful of the 
culture to be tested, taken from the top of the tube, and then six drops 
of Nessler’s solution was added to each tube of water and culture dilu¬ 
tion. The color of the tubes was observed by looking vertically through 
them upon a white background. No color developed in any of the tubes 
except in those containing some of the culture of B . phytophthorus 
from Schuster. The latter gave a distinct yellow color. 
Pethybridge and Murphy (26) have recorded the appearance of small 
amounts of gas in cultures of B. melanogenes in tubes of a 2 per cent 
potassium-nitrate broth having a plug of vaseline on the top. For the 
purpose of testing all of the organisms in this respect, fermentation tubes 
were filled with the nitrate broth described in the next section, sterilized 
by fractional steaming, and then inoculated. Growth appeared in these 
rather slowly but at the end of 48 hours all were uniformly though some¬ 
what faintly clouded with the exception of the two strains carried under 
the name of B. phytophthorus . These showed only growth in the bulb. 
Later they showed some clouding of the closed arm of the tube, but this 
was exceedingly faint in the case of B . phytophthorus from Appel. No gas 
whatever appeared in the closed arm of the tubes with any of the organ¬ 
isms studied. Tubes of this same broth, tested at the end of five days, 
with Nessler’s reagent by dropping five or six drops of the reagent directly 
into the tubes gave no qualitative test for ammonia, except in the case of 
B. phytophthorus from Schuster. Cultures of the latter when treated with 
the reagent produced a very distinct, yellow reaction. That the Nessler’s 
solution used was of good quality was indicated by the fact that it would 
produce the characteristic reaction in the presence of very minute quanti¬ 
ties of ammonia, artificially introduced into distilled water. 
In connection with these tests it should be noted that Pethybridge and 
Murphy used a 2 per cent potassium-nitrate broth, while the writer used 
that specified by the Committee on Standard Methods of Water Analysis, 1 
which carries only 2 gm. of potassium nitrate per liter. 
Where Nessler’s solution was added directly to young cultures in 
Dunham’s peptone solution, in no case was there any more color observed 
to result than where the uninoculated check tube of the same medium 
was so treated, except in the case of B. phytophthorus from Schuster. 
Cultures of this organism gave a yellow color reaction. 
Reduction oe nitrates. —Cultures in nitrate broth, consisting of 
2 gm. of chemically pure potassium nitrate, 1 gm. of Witte’s peptone and 
1 liter of water, were tested by the starch-iodin method after five days. All 
1 Report of committee on standard methods of water analysis to the laboratory section of the American 
Public Health Association, presented at the Havana meeting, January 9,1905. 141 p. Chicago, Ill., 1905. 
Reprinted from Jour. Infect, Diseases, suppl. 1,1905. 
