218 AIDS TO BACTERIOLOGY 



tinge. The growth on potato is a thick, dirty yellow layer, 

 which afterwards becomes blue; the medium is dis- 

 coloured. It gives an alkaline reaction in ordinary milk, 

 and does not produce coagulation. It usually yields two 

 pigments one of the ordinary fluorescent type, and the 

 other of a bluish to greyish colour, which becomes more 

 strongly blue up to azure in milk with an acid reaction. 

 Blue milk may also be caused by other organisms. 



Red Milk. Haemorrhage from the udder, B. prodigi- 

 osus, Sarcina rosea, or Saccharomyces ruber, may give 

 rise to red milk, and the last may cause infantile diarrhoea. 

 Generally B. lactis erythrogenes (Hueppe) is to be found 

 a short bacillus, liquefying gelatin. The colonies are of 

 a yellow colour when first seen, 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. In milk the red 

 coloration is developed best when the medium is slightly 

 alkaline and kept in the dark, and is checked by acidity 

 and light. On standing, the cream rises as a yellowish 

 layer and the casein is precipitated, though the reaction 

 remains alkaline and the clear serum is pink. 



Yellow Milk. The best-known organism causing this 

 disease is B. synxanthus, a motile rod, curdling milk by 

 means of a rennet-like ferment, which afterwards redis- 

 solves the curd and produces a yellow pigment. 



Bitter Milk may be due to the ingestion of certain 

 plants by the cow. Among the several organisms capable 

 of producing bitterness is the bacillus of Bleisch, a flagel- 

 lated, facultative anaerobe, rapidly liquefying gelatin, and 

 producing a thin, flat, greyish growth on agar and potato. 

 In milk it will, after a week, produce transparent yellow 

 streaks below the cream, the milk itself coagulating, and 

 the coagulum being subsequently, earlier or later, almost 

 completely dissolved. The bitter taste arises after the 

 second week; there is no smell; the reaction is acid. At 

 higher temperatures the milk becomes bitter, and gives 

 the biuret reaction after twenty-four hours, while spores 

 are produced which resist boiling for six hours. Conn's 

 micrococcus of bitter milk coagulates milk, and then pro- 

 duces a slimy solution, with a slightly sour and very bitter 

 taste. Trillat and Sauton found bitter milk to contain 

 aldehydes and ammonia. 



