Studies on Physiology of Some PiAnt Pathogenic Bacteria 
41 
of growth, in the agitated cultures, is correlated with increased acidity as 
would be expected. An intensification of activity, therefore of B. glycineum 
just as with Nitrosococcus and Azotobacter results from agitation. 
Another situation for which no explanation can be offered at this time ap¬ 
pears in the flasks containing 1 per cent of dextrose. Those which remain 
undisturbed undergo a reversal of reaction, such as is shown also in Table 
6 from which we concluded that 1 per cent dextrose in plain bouillon was in¬ 
sufficient to permit of the development of the characteristic final reaction. 
When cultures of the same dextrose content are agitated there is seen to be a 
progressive increase in acidity just as occurs with 2 per cent of this sugar or 
of saccharose. In the case of 1 per cent saccharose, however, when agitated 
and also when quiet, there is a reversal of reaction, beginning on the sixth or 
seventh day. 
If one contrasts, furthermore, the daily pH concentrations in this table with 
those in Table 7, the influence of initial reaction considered in Experiment 
VII will be apparent. 
SUMMARY 
Consideration is given, in this study, to the fermentative activity of Bacillus 
carotovorus, Bacterium tabacum, B. angulatum, B. glycineum, B. sojae and 
B. campestre, as influenced by initial reaction, concentration and kind of car¬ 
bohydrate, concentration of buffer material, and mechanical agitation. 
All are found to grow at a fairly uniform rate over a wide range of initial 
reaction. As this reaction approximates pH 5.0 and pH 9.0 as extremes, how¬ 
ever, a slight change in pH produces a marked effect upon cell multiplication. 
The rate of growth for these forms in terms of generations per hour varies 
between 0.25 and 0.5, which is considerably less than for forms from animal 
bodies. 
In plain broth cultures, there is a progressive increase in alkalinity with 
all organisms except B. carotovorus. This form shows at first an increase in 
acidity, which is followed by a reversal of reaction. This increase appears 
also in peptone broth and is believed, as has been pointed out by others, to be 
due to a selective action upon that part of the peptone molecule which reacts 
like a carbohydrate. 
The initial reaction of cultures of these organisms is one of the factors which 
exerts an influence in modifying the final reaction in any given medium. 
Each organism appears to require a definite concentration of carbohydrate 
in a given medium if it is to produce its characteristic final reaction. In the 
case of B. carotovorus, the optimum concentration lies between 0.1 and 0.3 
per cent with dextrose, saccharose, or lactose, and concentrations greater than 
0.3 per cent are without effect upon final hydrogen ion concentration. The 
corresponding optimum of dextrose and saccharose for Bacterium tabacum, 
B. angulatum, P». glycineum, and B. sojae lies between 1.0 and 2.0 per cent. 
A concentration of glycerine between 1 and 2 per cent appears to be optimum 
for B. carotovorus. This optimum is determined by the reversal of reaction, 
such as.occurs when insufficient fermentable sugar is present. 
The minimum concentration of carbohydrate is related to the concentration 
of buffer materials since increases of peptone, through its increased neutraliz¬ 
ing power, delays the production of the final level of acidity. 
Fermentable sugars are not attacked with equal vigor, since the rate and 
amount of fermentation vary both with the species of organism and the kind 
