CHANGES IN MILK 57 



producing a red color partly as spots and partly as a 

 diffuse discoloration covering the entire surface. The 

 Bacterium lactis erythro genes, isolated by Grotenfeldt, 

 coagulates milk and afterwards dissolves the coagulum 

 into a red fluid. 



Yellow milk is produced by a number of organisms 

 that cause the development of yellow or orange-colored 

 spots on the surface. Bacillus synxanthus is an exam- 

 ple of these organisms that are derived from the 

 atmosphere. 



Summary. Milk that is not sterile and that is left 

 to itself, usually undergoes lactic acid fermentation for 

 the reason that lactic acid bacteria are present in large 

 numbers, and by breaking up the milk sugar to form 

 acid, most of the other forms of bacteria are repressed 

 to a high degree. Curdled milk may have a clean, sour 

 taste, or a more or less unpleasant, bitter, offensive or 

 oily taste. The latter condition comes from either 

 simultaneous development of other bacteria or from the 

 peculiar effects of special lactic acid bacteria which have 

 caused the acid formation. Coagulated milk left to itself 

 is usually quickly covered with a thin, whitish, consist- 

 ent layer formed of milk moulds {Oidium lactis) and, 

 not infrequently, colored spots appear that are caused 

 by bacteria or fungi, as Penicillium glaucum. By 

 degrees the coagulated milk undergoes a putrefactive 

 transformation accompanied by a foul-smelling disin- 

 tegration of the casein. 



Less frequently, the milk quickly becomes slimy or 

 stringy before it has become acid, or while it is begin- 

 ning to sour. Or it may early acquire a bitter taste 

 and an unpleasant, loathsome odor; very often it does 

 not sour and coagulate, but gradually putrefies: the 

 usual lactic acid fermentation has not appeared and 

 checked the increase of the bacteria of putrefaction. 



