40 
North Carolina Agricultural Experiment Station 
Experiment VIII—Changes in Reaction as Influenced by Mechanical 
Agitation 
Recent studies by Bonazzi (5) have shown that more vigorous growth and 
greater physiological activity by Nitrosococcus may be induced by mechanical 
stirring of the culture solutions. He does not enter into any speculation as to 
the cause aside from mentioning the possibility that shaking may provide bet¬ 
ter aeration or assist in the removal of by-products unfavorable to growth. 
Allen (1) employing this fact found that this type of treatment is beneficial 
also in cultures of Azotobacter. Their agitating device was so constructed as 
to hold the culture flasks in a horizontal position and revolve them with a uni¬ 
form, slow motion. The present series, which is summarized in Table 12, 
was based upon the results of Bonazzi and Allen. Flasks containing 150 cc. 
of bouillon of the appropriate carbohydrate concentration were prepared and 
inoculated with B. glycineum. The initial reaction of the dextrose broths was 
pH 7.2, and they were maintained at a temperature of 20°-25°C., while the 
initial reaction of the saccharose broths was pH 7.8 and they were incubated 
at 28° C. An initial volume of bouillon of 150 cc. in 250 cc. flasks was employed. 
At twenty-four hour intervals, 5 cc. quantities were withdrawn with aseptic 
precautions from each flask, for the pH determinations. The flasks which were 
agitated were attached to a platform which was devised to be used with the 
Leeds and Northrup shaking apparatus. This machine, which is a part of 
their apparatus for the electrometric measurement of hydrogen ion concen¬ 
tration, imparted a rocking motion to the flasks. The check culture flasks 
were of course placed on a shelf where the solutions could remain quiet. 
Table 12.— Influence of Agitation of Cultures of Bacterium Glycineum in 
Dextrose and Saccharose Bouillon on Changes in Reaction 
Age in Days and pH Concentration 
Days 
of 
Carbohydrate 
1 
2 
3 
4 
5 
Agi¬ 
tated 
Quiet 
Agi¬ 
tated 
Quiet 
Agi¬ 
tated 
Quiet 
Agi¬ 
tated 
Quiet 
Agi¬ 
tated 
Quiet 
pH 
pH 
pH 
pH 
pH 
pH 
pH 
pH 
pH 
pH 
Per c,ent of 
dextrose: 
1.0 _ 
6.6 
6.6 
6.2 
6.4 
6.0 
6.6 
5.6 
7.0 
5.2 
7.4 
2.0 _ 
6.2 
6.6 
5.6 
6.2 
5.4 
5.8 
5.2 
5.6 
5.0 
5.2 
Per cent of 
saccharose: 
1.0 _ 
7.4 
7.8 
7.2 
7.6 
7.0 
7.4 
7.4 
7.0 
7.6 
6.8 
2.0 _ 
7.4 
7.6 
7.2 
7.2 
6.2 
7.0 
5.8 
6.6 
5.8 
6.4 
B. glycineum, it should be remembered, is of the type of organism which 
tends to form a surface pellicle for which reason, it was selected for this ex¬ 
periment. The most striking feature which it exhibits when agitated is the 
increased rate of growth as evidenced by the clouding of the broth. This con¬ 
dition obtains with both dextrose and saccharose bouillon. This increased rate 
