3-74 Bacteria in Relation to Country Life 



activities of the lactic-acid organisms are enhanced by 

 the accompanying non-acid species in other ways. It 

 has been found for Bacillus casei E, that aerobic bacteria 

 promote its development and hasten the souring of milk 

 by using up the oxygen in the liquid. Anaerobic con- 

 ditions suitable for this organism are thus produced. 



MILK FAULTS 



When organisms other than the lactic-acid bacteria, 

 or even certain of the less common lactic-acid bacteria, 

 gain the upper hand in the milk, changes may occur 

 that render the milk unattractive in appearance, un- 

 pleasant to the taste or smell, or even dangerous to 

 health when consumed in larger quantities. Such abnor- 

 mal changes in milk are known as milk faults, or milk 

 diseases. Milk faults, well known in olden times, were 

 then more common than they are today because of the 

 less adequate means for cleaning and disinfection. 

 Blue milk, bitter milk, slimy or ropy milk, red milk, 

 and many other kinds, frequently caused much annoy- 

 ance in dairies. Unfortun^ely, some of them occur, 

 but too frequently at present. 



Blue milk. — This was the first of the milk diseases 

 to be studied carefully. Its bacterial origin was sus- 

 pected before the middle of the last century. It is mani- 

 fested usually in warm weather, within one to three days 

 after the milk is drawn, by the appearance of bluish 

 spots on the surface and their gradual spread until the 

 entire surface assumes a blue color varying in intensity. 



The organism producing this fault has been isolated 



