THE KINDS OF MICRO-ORGANISMS IN MILK 



349 



milk, and the souring is produced by the activity of both. Hiippe's 

 Bacillus acidi lactici, therefore, is, in reality, B. aerogenes, and 

 Leichmann's Bacterium lactis acidi is Streptococcus lacticus. 



Streptococcus lacticus is now almost universally recognized as 

 the lactic acid bacterium par excellence. We have learned that 



Fig. 166, e. Streptococcus lacticus 

 from lactose broth. (Strain I.) 



Fig. 166, /. Streptococcus lacticus 

 from lactose broth. (Strain II.) 



Fig. 166, g. Streptococcus lacticus 

 from litmus milk. (Strain I.) 



Fig. 166, h. Streptococcus lacticus 

 from litmus milk. (Strain II.) 



Fig. 166, a-h. Microphotographs of Streptococcus pyogenes and Streptococ- 

 cus lacticus, showing the tendency to diplococcus formation in litmus milk. 



the bacteria of milk are invaders and not indigenous, and it is 

 therefore reasonable to assume that lactic acid bacteria are also 

 derived from outside sources. They can be identified easily with 



