THE KINDS OF MICRO-ORGANISMS IN MILK 379 



tion is favored by the presence of acid. Large blue spots of the 

 size of a dollar are formed on the surface of milk by this organism. 

 Whether this is a type distinct from Bacillus cyanogenes or merely 

 a variation is not known. 



Wolff mentions Bacterium indigonaceum as an organism pro- 

 ducing bluish-green milk; Bact. cseruleum, producing a sky-blue 

 cream; Bacillus violaceus, which does not color the whole milk, 

 but forms a blue film, and Bacillus membranaceus amethystinus. 

 Descriptions are too meager to classify these organisms. 



Weigmann has isolated a species of oi'dium that produces a 

 blue color in milk. Tlie author made the interesting observation 

 that the pigment is not carried by all cells composing a filament 

 of the mold, but that colored cells occur intermittently within the 

 threads. 



RED MILK 



As a rule, red pigments develop in milk less rapidly than blue 

 pigments. The red color appears generally after, a lapse of two 

 to three days, so that the milk is delivered to the consumer in 

 apparently good condition. When milk is colored red from the 

 presence of blood the color naturally appears immediately after 

 milking. 



Red milk is probably caused by Bacillus prodigiosus more fre- 

 quently than by other red pigment-forming micro-organisms. 

 Usually the cream alone appears colored as the bacteria rise with 

 the fat globules. Such milk is, of course, entirely harmless and 

 objectionable only on account of appearance. 



Bacillus erythrogenes, first described by Hiippe, sometimes 

 imparts a red color to milk. The red color is then diffused through- 

 out the whole volume of the milk. Other organisms mentioned 

 by Weigmann that occasionally cause red milk are Bacillus lacto- 

 rubefaciens (Gruber), Sarcina rosea, and Micrococcus cerasinus 

 (Keferstein). 



OTHER COLORED MILKS 



Bacillus fluorescens is a common inhabitant of water and feces, 

 and consequently of milk. Its fluorescent pigment, however, ap- 

 pears but rarely, since the acid prevents its formation. Yellow 

 milk is very uncommon, although a few accounts may be found 

 in the literature. Sarcina lutea may form a yellow pigment in 

 milk, but the pigment settles and does not impart a yellow color 

 to the whole milk. Bacterium synxanthum produces a pigment 

 that diffuses throughout the milk. This organism is a small, 

 motile bacillus that coagulates milk and dissolves the casein, leav- 

 ing a lemon-yellow fluid. 



