378 MILK 



boiled milk. As a matter of fact, boiled milk does not usually 

 sour. 



Bacillus cyanogenes or Bacterium syncyaneum is probably the 

 most common cause of blue milk. It has been isolated and de-, 

 scribed by authors in this country as well as in Europe, and, 

 therefore, may be assumed to be widely distributed. The color 

 is not produced in milk kept at 37 C., according to Hammer, 

 who has made an exhaustive study of some strains of this organ- 

 ism. The distribution of the color seems to be more uniform 

 throughout the volume of the milk when the milk has been pas- 

 teurized than when raw. 



Bacillus cyanogenes is an actively motile rod; it is readily dis- 

 colored by Gram's method of staining; according to some authors 

 (Weigmann, Hammer) the organism does not produce spores, 

 while others (Conn, Esten, and Stocking) claim to have observed 

 spore formation. On agar, pigment does not develop, but in old 

 cultures a brownish color appears near the puncture. Surface 

 colonies are large and appear somewhat bluish. Gelatin is not 

 liquefied, but casein seems to be broken up in a moderate degree. 

 Hammer states that a most intense blue color develops in dextrose 

 broth; a bluish-green in glycerin broth, and a brownish tinge in 

 levulose broth. Broth containing either sucrose, mannit, raffinose, 

 or lactose turns slightly brown, while with maltose, salicin, or 

 inulin a greenish tinge is observed. No pigment develops on 

 potato. Bacillus cyanogenes does not produce gas from carbo- 

 hydrates and does not grow in the closed arm of a fermentation 

 tube. According to Hammer, acid is produced from dextrose, 

 but not from other carbohydrates. 



Blue milk has been observed more frequently in summer than 

 in winter. Weigmann states that feeding of turnips or of clover 

 mixed with horsetail (Equisetum arvense) causes the blue pigment 

 to appear in milk, and that a change of food relieves the trouble. 

 The micro-organisms producing the pigment are said to be dis- 

 seminated by the foods mentioned, and consequently they are 

 also present in cow feces, and may gain access to the milk from 

 this source. 



The pigment of Bacillus cyanogenes as it appears in milk, 

 according to Weigmann, is composed of two pigments, namely, 

 a steel-blue and a fluorescent one. The fluorescent pigment is 

 intensified by presence of magnesium sulphate, while phosphates 

 favor development of the blue pigment. 



Bacillus cyaneofluorescens is sometimes mentioned as causing 

 blue milk. This organism is a small, motile bacillus with terminal 

 flagella, and does not form spores. Gelatin is not liquefied and 

 an odor of trimethylamin develops in cultures. Pigment forma- 



