2/0 FERMENTATIONS IN MILK 



environment, the term species as used when dealing with 

 the higher plants and animals cannot be applied with 

 any degree of precision. Well-marked, permanent, or 

 constant differences which the term implies do not exist 

 among the lactic bacteria. In the present state of 

 knowledge it is, therefore, perhaps best to place those 

 which have been described in groups according to the 

 presence or absence of certain characters which are 

 subject to comparatively little variation, the name of 

 each group being that of one of the most distinct forms 

 represented in it. 



General Characters of lactic bacteria Most of 

 the lactic bateria met with in milk and its products are 

 cocci or short-rods, and are non-motile. They are with- 

 out the power of spore formation, and consequently 

 liquids containing only these forms are easily rendered 

 sterile by heating to boiling point. Some forms of the 

 lactic bacteria grow well enough on gelatine, while others 

 exhibit feeble growth upon this or any other solid 

 medium. Their colonies are generally either white or 

 yellowish-white, and do not liquefy gelatine. They pro- 

 duce lactic acid in milk, especially at elevated tempera- 

 tures, and usually curdle it sooner or later. -Some grow 

 well in the presence of oxygen, others, perhaps the 

 majority of kinds, are facultative anaerobes. 



The following groups suggested by Lohnis may be 

 recognized, viz.: . 



Group i. Streptococcus lacticus, Kruse. 

 ii. Bacterium acidi lactici, Hiippe. 

 iii. Bacterium casei, Freudenreich. 

 iv. Micrococcus lactici acidi, Marpmann. 



The typical bacteria of groups i. and ii, are the most 



