ALKALI-FORMING BACTERIA FOUND IN MILK. 35 
subgroup 11. Another noticeable secondary characteristic was the 
uniform limiting P H value in dextrose medium A, the composition 
of which was given on page 13. Each subgroup of the dextrose 
fermenters utilized the carbohydrate to a practically constant limit- 
ing hydrogen-ion concentration, as is shown for example in subgroup 
10, where all the 6 cultures fermented dextrose to P H 6.2 after 7 
days' incubation at 30° C. The reaction in milk was similar in sub- 
groups 4, 5, and 6. In these 3 groups there was first a primary alkali 
fermentation which was followed by what was apparently a second- 
ary acid fermentation, during a period of 30 days' incubation. The 
secondary characteristics of this group have been given in detail so 
as to emphasize further and show the possibility of the new method of 
grouping alkali-forming bacteria according to their ability to utilize 
carbon when supplied in a synthetic medium from organic-acid salts, 
carbohydrates, and alcohols. It was impossible to make this study 
cover all types of the alkali-forming bacteria, because the definition 
chosen for this group is so simple and yet so comprehensive that it 
must include a very large number of species of bacteria. Therefore, 
the scheme for grouping this particular collection of alkali-forming 
organism is not intended for a definite classification of all the alkali- 
forming group of bacteria. It should serve, however, as a possible 
basis for future work along this line and particularly to draw attention 
to the fact that the fermentation of organic-acid salts is a reliable and 
important means for classification, especially for organisms of this 
type occurring in soil. 
SUMMARY AND CONCLUSIONS. 
1. The alkali-forming bacteria may be defined as those bacteria 
which produced an alkaline reaction in milk without visible signs of 
peptonization. In litmus milk this reaction appeared sometimes 
within 48 hours, usually within 5 days, while occasionally a longer 
period was required. The alkaline reactions were caused primarily 
by the oxidation of the salts of citric acid to alkaline carbonates. 
Other organic-acid salts if present in milk may also be similarly 
fermented. Ammonia played little or no part in causing the alkaline 
reaction during the first 7 days of incubation, but at later periods 
a few cultures produced considerable ammonia. Several cultures 
showed a primary alkaline fermentation which was followed by what 
was probably a secondary acid fermentation. 
2. The alkali-forming bacteria studied were isolated principally 
from milk, a few being obtained from ice cream. These organisms 
were found in large numbers in numerous samples of soil and also 
water. They were present in large numbers on the hands of farm 
laborers, and in unsterilized milk utensils. While not present in 
the udders of cows, the alkali-forming bacteria were present in 
relatively small numbers in cow feces. It seems evident that the 
