136 OUTLINES OF BACTERIOLOGY 



Bac. lactis erythrogenes or Sarcina rosea. When other food stuffs, 

 such as cheese, boiled carrots, or boiled meat become covered with 

 red spots, the cause of the malady is, in most cases, traceable to Bac. 

 prodigiosus, each spot being a colony of this microbe which, as just 

 mentioned, shows great adaptability, and can attack a variety of food 

 stuffs. 



3. Bacteria producing Yellow Colouring Matters. A large number 

 of organisms belonging to the Sarcina group possess the power of 

 secreting yellow colouring matters : among these may be mentioned 

 Sarcina ventriculi, the first to be discovered of that group, Sarcina 

 flava, Sarcina mobilis, Sarcina lutea, and many others. Also they are 

 not wanting in other groups ; thus Bacillus synxanthus is sometimes 

 responsible for the production of "yellow" milk that is, milk which 

 turns yellow on standing. This malady occurs only in milk that has 

 been boiled, so that its growth is probably prevented in unboiled milk 

 by the multiplication of the lactic-acid bacteria which are so abundant 

 in milk, and which are killed when this liquid is boiled. The colouring 

 matter of this microbe is insoluble in alcohol and ether, but soluble 

 in water. It is not affected by alkalies, but acids seem to have the 

 power of combining with it to form a colourless compound. Of the 

 large number of bacteria which secrete yellow colouring-matters, almost 

 all are harmless saprophytes. 



4. Bacteria producing Blue Colouring Matters. Among the bacteria 

 which produce blue colouring matters one, Bacillus lactis cyanogenus, 

 has been known a long time, and extensively studied on account of 

 its frequent occurrence in milk, to which it imparts a blue coloration 

 when present in excessive numbers. The coloration appears in from 

 twenty-four to seventy -two hours after the milk has been drawn from 

 the cow, the process being hastened in warm weather and retarded in 

 cold weather. The individuals of this species are short, actively 

 motile rods, which have the power of forming endospores. The 

 average breadth of an individual has been given as 0-3-0-5 /x and the 

 average length 1-4 /x. A very small amount of acid is sufficient to kill 

 it, consequently it never attacks sour milk, and when present in sweet 

 milk stops growing when this turns sour. This microbe grows equally 

 well in the milk of the cow, ewe, goat, mare, ass, and dog, and also 

 in human milk. It likewise feeds on many other articles of diet, such 

 as rice, potatoes, etc., and is in consequence very widely distributed. 

 Fortunately it is not pathogenic, and its chief objection is that it gives 

 to articles of food, especially to milk, an unappetising appearance. The 

 colouring matter is excreted outside the cell (chromoparous). 



