324 APPLIED BACTERIOLOGY 



employed at the time. The bacillus of 'blue milk' is 

 known as the Bacillus cyanogenus. 



B. cyanogenus. — The bacillus of blue milk consists of 

 small motile rods, which are provided with abundant 

 flagella. The organism is pale blue in colour, does not 

 liquefy gelatine, which, however, is stained bluish-green, 

 finally becoming of a dirty grayish tinge. On potatoes 

 the growth occurs as a thick, dirty-yellow layer, which 

 afterwards becomes blue ; the medium is discoloured. 



Red Milk. — Several organisms may give rise to this 

 disease in milk, the chief of which is the red milk bacillus 

 of Hueppe {B. lactis erythrogenes). 



B. lactis erythrogenes. — This organism was isolated by 

 Hueppe and Grotenfeldt from red milk. It occurs as short 

 rods, the growth of which liquefies gelatine. The colonies 

 are of a yellow colour when first seen on the plate, but 

 after liquefaction they become rose -red. A yellowish 

 deposit occurs on agar, which soon changes to yellowish- 

 red. The cultures give rise to an unpleasant, sweet smell. 

 Other organisms which give rise to red milk are the 

 following : B. prodigiosus, Sarcina rosea, Saccharomyces 

 ruber (pink torula). A red colour in milk may be due to 

 the presence of blood, as a result of disease of the udders. 



Yellow Milk. — According to Freudenreich many organisms, 

 especially those of putrefaction, can produce a yellow colour 

 in milk, but this is rare in practice, as the milk is very 

 seldom kept long enough for this change to take place. 

 The best-known organism which gives rise to a yellow 

 colour in milk is the Bacillus synxanthus. This organism 

 ■was first found in a sample of boiled milk which had 

 assumed a yellow colour. It is a motile rod, which curdles 

 milk by means of a rennet-like ferment, which afterwards 

 re-dissolves the curd and produces a yellow pigment. 



Bitter Milk. — This fault may be produced in milk by the 



