BLUE MILK BACTERIA. 87 



COLORED MILKS. 



There are a number of somewhat rare fermentations in 

 milk, each due to the action of microorganisms, each charac- 

 terized by the development in the milk of certain pigments 

 which change its color. These occasionally appear as dairy 

 infections, but in ordinary dairying they will rarely be met. 

 Inasmuch as they do occasionally appear, however, a brief 

 reference to them must be made. 



Blue Milk. The oldest known form of such fermentation 

 is blue milk. This was carefully studied as far back as 1841, 

 by Fuchs (84), and it is interesting as being the first fer- 

 mentation that .was proved to be associated with and caused 

 by bacteria. Milk affected with this trouble does not sour 

 normally, but, about the time it begins to become acid, 

 blue spots develop in it, extending rapidly through the milk, 

 and by the time the milk has become thoroughly acid it has 

 also turned to a sky-blue color. The blue coloring material 

 does not appear to be at all injurious, or even to render the 

 milk unwholesome, but, of course, it spoils the milk for 

 all commercial purposes. This trouble has been found to 

 be due to a definite species of bacterium called B. cyano- 

 genes, a species capable of producing this infection when 

 inoculated into milk along with lactic acid bacteria. A 

 second species has in more recent times been discovered with 

 similar properties and called B. cyanofluorescens (87). 



The blue milk infection occasionally appears in dairies 

 and may spread from one dairy to another. It has been 

 traced to individual cows in a herd and checked by removing 

 the milk of these cows. The only remedy is the general 

 one for all such troubles, namely, cleaning and sterilizing all 

 vessels, the dairy and everything that comes in contact 

 with the milk. The blue milk organism is an unusual one, 

 and with cleanliness and disinfection the dairyman may 

 hope to get rid of it. In one case the trouble was cured by 



