ABNORMAL MILK. 57 



fully, be mistaken for colostrum. Bloody milk produced by an 

 inflamed udder, may be distinguished by noticing small blood 

 particles, which will settle to the bottom, and can be noticed if 

 the sample is placed in a glass test-tube. Bloody milk caused by 

 bacterial growth does not show the blood at the bottom, but 

 instead, previous to stirring the milk or cream, it appears on 

 the surface in small red dots. The red color which commonly 

 occurs in milk is due chiefly to a species of germ called Micro- 

 coccus prodigiosus. Colostrum will show reddish cream on the 

 surface, but no blood-like material will separate out. 



Blue Milk. Blue milk is quite commonly found. Formerly 

 it was thought that this color was due to the condition of the 

 casein in the milk, but since more has been discovered in regard 

 to the effect of germ life upon conditions and properties of milk, 

 it has been proved that blue milk is caused by bacteria* (Bacil- 

 lus cyanogenus). This particular germ produces the blue color 

 in the milk only when the milk has an acid reaction. When 

 sterile milk is inoculated with this particular germ, the blue 

 color is not produced, but by the addition of a little acid, or by 

 inoculating the milk with the bacteria that produce lactic acid, 

 the blue color is produced. This seems to be one of the instances 

 of symbiotic action of bacteria in milk. There are probably 

 other causes, but they are not known. This germ, according 

 to Aikman, is killed by heating the milk to about 176 F. The 

 germ ceases to work as soon as milk is coagulated. 



Yellow Milk. According to Aikman,* yellow milk is caused 

 chiefly by one species of bacteria, named Bacillus synxanthus. 

 This micro-organism belongs to the group of ferments that act 

 upon the fat of milk. There are different shades of yellow 

 produced in milk, caused by different species of bacteria, but 

 the above-mentioned one is considered to be the principal cause. 

 Some produce a brilliant yellow color, while other species first 

 curdle the casein, and then digest or dissolve it into a yellow 

 or amber-colored liquid. 



* C. M. Aikman, in "Milk, Its Nature and Composition." 



