2 BULLETIN 782, U. S. DEPARTMENT OF AGRICULTURE. 
Bacillus fsecalis alJcaligenes of Petruschky, also Bacillus No. 66 
described by Conn (4) . B. fsecalis alJcaligenes described by Petru- 
schky (8) is well known as an organism which turns milk distinctly 
alkaline without producing any other apparent change. This is the 
characteristic reaction of the alkali-forming group of bacteria which 
separates them distinctly from other organisms which turn milk 
alkaline and cause peptonization at the same time. 
Seiffert and Wymer (9) in 1912 reported alkali formation in litmus 
medium caused by bacteria which used proteins only to the smallest 
extent for this reaction, the chief source being citric acid and lactic 
acid produced by cleavage from the lactose. Both of these acids 
were decomposed to the alkali carbonates or bicarbonates. 
Unfortunately it has been and still is the custom of most bacte- 
riologists to consider all organisms which produce an alkaline reaction 
in milk as alkali-forming bacteria. It is generally assumed that the 
alkaline change is due to the formation of ammonia which is formed 
from the decomposition of the protein. Consequently when the 
alkali-forming bacteria are mentioned, the ammonia-producing, 
peptonizing types are usually brought to one's mind. Since the 
alkali-forming bacteria as they are considered in this paper include 
only those bacteria which produce an alkaline reaction due to the 
formation of carbonates or bicarbonates, it is necessary to define the 
limits of this group. 
DEFINITION OF THE ALKALI- FORMING GROUP OF BACTERIA. 
The alkali-forming bacteria are characterized by ability to pro- 
duce an alkaline reaction in milk without visible signs of peptoni- 
zation. This reaction is due to the oxidation of the salts of the organic 
acids present in milk to alkaline carbonates. In litmus milk the 
alkaline change is usually noticeable within 5 days when incubation 
is at 30° C. Often the change may be seen in 48 hours and occa- 
sionally a period of incubation longer than 5 days is necessary before 
it appears. 
CAUSE OF THE ALKALINE REACTION IN MILK. 
The alkaline production in milk during a period of 7 days' incuba- 
tion at 30° C. is believed to be due almost entirely to formation of 
alkaline carbonates from the oxidation of the salts of organic acids, 
presumably citric acid, since fresh milk was used. This belief is 
based on the following facts: First, it was found that a number of 
the cultures tested used up all the citric acid in milk within a period 
of 7 days when incubated at 30° C, during which period the milk 
changed to reaction toward the alkaline side; and second, only a few 
cultures produced any ammonia in milk during a period of 7 days' 
