ALKALI-FOKMING BACTEKIA FOUND IN MILK. 9 
which was previously stated, namely, that the alkali-forming 
bacteria produce an alkaline change in milk, due primarily to the 
formation of carbonates or bicarbonates, resulting from the oxida- 
tion of citric acid. After a long period of incubation there is a small 
amount of ammonia formed by certain cultures to which may be 
attributed a small part of the alkaline change in reaction of milk. 
A third reason to substantiate the belief that the alkaline reaction 
in milk produced by the alkali-forming bacteria is due to the pro- 
duction of alkaline carbonates from the salts of organic acids. This 
will be discussed in detail later. The essential point of the produc- 
tion of an alkaline reaction during the fermentation of the organic-acid 
salts and the one upon which the other adjustments of equilibrium 
depend is the replacement of the relatively strong organic acids by 
the relatively weak carbonic acid. 
SOURCES OF THE ALKALI-FORMING BACTERIA. 
The alkali-forming bacteria which are under discussion in this 
paper were isolated largely from market milk, a few being obtained 
from the ice cream. Milk, however, can not be considered a source 
of any bacteria for it is merely a conveyor in which they may grow 
after being introduced through contamination. While alkali-forming 
bacteria are commonly found in market milk they must be intro- 
duced at some stage in its history and must, therefore, have a source. 
Numerous samples of soil were first examined and then plated on 
extract agar and incubated at 30° C. for 5 days, at which time each 
colony was picked off and inoculated into litmus-milk tubes. These 
tubes were incubated at 30° C. for 14 days, after which they were 
examined for the characteristic reaction produced by bacteria of the 
alkali group. An alkaline reaction in litmus-milk tubes after 14 
days' incubation without any sign of peptonization was found to be 
a practically certain test for the alkali-forming group of bacteria. 
All the samples of soil examined showed the presence of large 
numbers of alkali-forming bacteria. These organisms were found 
also in water from shallow and deep wells, springs, and drains. 
Since they are present in soil it is only natural to expect to find 
them in water. An examination of the bacteria on the hands of 
farm laborers showed as high as 12,000,000 of the alkali-forming 
group of bacteria, this being the approximate number distributed 
over both hands. The organisms in this case in all probability came 
from soil. 
Alkali-forming bacteria were not found in the udder and teats of 
cows in very large numbers, since an examination of 57 samples of 
milk drawn into sterile tubes from 15 different cows showed their 
presence in only 10 cases. The highest number found in any case 
was 30 per cubic centimeter. These organisms were present, how- 
104410°— 19— Bull. 782 2 
