350 MILK 



well-known types that are widely distributed in nature and 

 especially in the dairy. 



The influence of Streptococcus lacticus on milk is desirable 

 from the butter and cheese makers' viewpoints. While pre- 

 dominance of Bacillus aerogenes produces off flavors in dairy 

 products, most strains of Streptococcus lacticus produce desirable 

 flavors. Butter starters, as a rule, are pure cultures of Str. lacticus. 



The distribution of the two groups of lactic acid organisms in 

 nature has been investigated to some extent. Barthel found 

 Streptococcus lacticus widely distributed on meadows, plants, 

 and cultivated lands, but scarce and in enfeebled condition on 

 wooded land. In the dairy he found it in cow manure, in the 

 dust of the air, in water, very commonly on the coat of the ani- 

 mal, on hay, straw, in oil cake, bran, malt, and even on fhes. 

 The occurrence of Streptococcus lacticus in cow manure explains 

 its constant presence in milk. In fact, the writer was able to 

 produce souring of milk which closely resembled the "normal" 

 souring by inoculating sterile milk with small quantities of cow 

 manure. 



Holling isolated streptococci from the feces of infants, horses, 

 and other domestic animals, and was able to show that sterile 

 milk coagulated typically when inoculated with these organisms. 



Bacillus coli has been found by Prescott practically as widely 

 distributed as Streptococcus lacticus. He found it on grains, 

 plants, and cereals, so that its common occurrence in nature has 

 been demonstrated. Whether Bacillus aerogenes shares in this 

 wide distribution is not known. It has been reported that Bacil- 

 lus aerogenes is more common in cow manure that B. coli, but 

 Rogers states that "the B. coli type is found abundantly in bovine 

 feces, while the B. aerogenes type is very rare." Further investi- 

 gation of this subject is desirable. However, there is no question 

 about the occurrence of both Bacillus coli and B. aerogenes in 

 cow manure, and, consequently, they are almost universally pres- 

 ent in milk. 



Rogers found that "through its greater resistance to the 

 unfavorable conditions found in water the Bacillus aerogenes type 

 is able to survive longer than B. coU." It is conceivable that a 

 similar state of affairs obtains in milk, inasmuch as milk may offer 

 more favorable food conditions for Bacillus aerogenes than for 

 B. coli, with the ultimate result that the former type prevails. 

 However, this is hypothetic, and the term "BacUlus coli group" 

 is intended to include both types. 



In the "normal" souring of milk both groups, the Bacillus 

 coli and the streptococcus groups, are active agents. It may be 

 assumed that immediately after milking these two groups are 



