2 BULLETIN 782, U. S. DEPAKTMENT OF AGKICULTUEE. 



Bacillus fsecalis alkaligenes of Petruschky, also Bacillus No. 66 

 described by Conn (4). B. fspxalis alkaligenes 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' 



