80 BACTERIOLOGICAL, EXAMINATION OF MII<K. 



pears under the action of acids and is restored by neu- 

 tralizing the acid with an alkaH. It is insoluble in alcohol 

 and ether. Yellow milk has a sickening odor and taste. 

 ?. Blue Milk. The Bacillus cyanogenus, Bacillus 

 cyaneofluorescens Zangemeister, and Bacillus janthinus, 

 all impart a blue color to the milk. 



(a) The Bacillus cyanogenus or Bacillus' syncyaneus 

 is a small rod frequently grouped in twos. Numerous 

 fiagella on the sides give it a vigorous motion. The bacil- 

 lus grows readily on slightly acid media, best at room 

 temperature. Gelatine plate cultures show superficial 

 colonies and stick cultures exhibit dark gray layers. It 

 grows well on media containing grape sugar and glycer- 

 ine. Sterilized milk becomes slightly alkaline and blue 

 gray. Unsterilized milk becomes dark blue. This bacillus 

 does not otherwise tend to decompose the milk. , Its ac- 

 tivity being dependent upon the formation of pigments. 



(b) Bacillus cyaneofluorescens Zangemeister differ 

 very sharply from the above. It is short and oval in 

 shape, motile, does not liquefy gelatine, but gives it a 

 yellowish green fluorescence. Upon sugar gelatine it 

 grows as a white film. The cultures have a strong odor 

 of trimethylamine. Unlike Bacillus cyanogenus, it 

 does not effect sterilized milk, but gives it a blue color 

 when inoculated together with the Bacillus acidi lactis. 



(c) Bacillus janthinus, a rod, grows on gelatine plates 

 as a white film, gradually becoming violet at the border. 

 The stick culture is violet only on the upper s'urface. On 

 potato a violet colored layer is formed. Sterilized milk 

 shows blue spots on the cream-surface. After a short 

 time the casein is precipitated, an alkaline reaction is 

 shown and an abundant amount of ammonia is formed. 



/j.. Stringy Milk. The micrococcii of Schmidt-Muhl- 

 heim give milk a slimy property, capable of being drawn 



