369 
The chemical nature of the blue pigment was not determined. The 
organism ordinarily responsible for the production of blue milk is 
known as Bacillus cyanogenes. When grown in fresh milk the effect 
produced by this organism is very striking. During the first few 
hours however no change is noticeable. A certain amount of lactic 
acid seems to be necessary for the formation of the blue substance 
resulting from the growth of this organism. As the milk turns sour 
therefore blue patches appear, until finally these may be distributed 
throughout the whole of the milk, in such cases imparting to it a sky- 
blue color. Still other organisms besides B. cyanogenes seem to have 
the power of producing blue substances in milk. 
Red milk . — According to Conn (31), red milk is by no means un- 
common in the dairy. Ordinarily, however, the red color of such 
milk does not result from the growth of bacteria, but is due to the 
presence of blood in the milk resulting from injuries to the udder. 
Sometimes it results from the feeding of the cow on plants containing 
red pigment, such as the madder plant, etc.; more rarely from a 
peculiar fermentation induced by bacteria. Among the organisms 
known to produce this change in milk may be mentioned Bacillus 
erythrogenes , B. prodigiosus , and a sarcina. The production of red 
milk through the agency of bacteria is without practical significance. 
Other color changes in milk . — Still other changes have been found 
to occur in milk and practically all of the pigment- forming bacteria 
will develop their characteristic pigments in milk in the event that 
they gain access thereto. According to Conn (31) orange-colored 
milk, green milk, yellow milk, amber-colored milk, indigo milk, 
chocolate-colored milk, and black milk have all been described by 
bacteriologists. In all cases the pigment has been found to have 
been produced by bacteria. These have been isolated and their mor- 
phological characteristics determined. Ordinarily they are not nor- 
mal infections, and hence are of no practical importance in dairying. 
Slimy or ropy milk. — Under certain conditions, slimy, mucilagin- 
ous substances are produced in milk through the growth of certain 
organisms which impart to the milk a characteristic sliminess or 
ropiness. Milk possessing such properties is known as slimy or ropy 
milk. It often can be drawn out into long threads of exceeding 
fineness. For example, slimy milk has been obtained of such vis- 
cosity that it could be drawn out into threads 10 feet in length and 
of such fineness as to be %3arcely visible. In certain countries slimy 
milk is esteemed a delicacy, and special methods have been de- 
vised for its preparation. Such is the case in Norway, where it is 
called by the natives “ taetamoelk.” In Holland also a special fer- 
1414 — Bull. 56—09 24 
