154 DAIRY FARMING 



these is blue. It is, however, not often met with in dairy 

 practice since the color usually does not appear until the 

 milk is several days old. The specific organism that 

 causes blue milk has been known for more than half a 

 century and is called cyanogenous. Another color that 

 rarely turns up in dairy practice is produced by a germ 

 known as prodigiosis, causing milk to turn red. Other 

 colors are produced such as yellow, green, and black, but 

 these are of very rare occurrence. 



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Microscopic appearance of pure and impure milk. A, Pure milk ; B, after 

 standing in a wash room for a few hours in a dirty dish, showing, besides 



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