362 
cheese. These peculiar odors and tastes were found to be due to 
specific bacteria, which were isolated and their morphological char- 
acteristics determined by these authors. 
Blue milk . — Under certain conditions a blue pigment may develop 
in milk as a result of peculiar changes set up by certain micro-organ- 
isms. While such milk is apparently harmless, it results from outside 
contamination and rarely if ever occurs in well-kept dairies. In one 
instance its production has been traced to some source of filth or un- 
cleanliness and in some instances to a single cow. Its occurrence may 
be prevented by the adoption of cleanly methods and in case it has 
been traced to any particular cow by washing the cow’s teats with a 
little weak acetic acid. It is of interest to note that blue milk is the 
first dairy infection definitely traced to bacteria. As early as 1841 
Fuchs (27) traced the production of blue milk to the growth of a 
micro-organism. By using Koch’s gelatin method Hueppe and Eng- 
ling (28) succeeded in isolating the organism which produces blue 
milk. It was found by these authors to produce different colors when 
grown on different media, but in solutions containing ammonium 
lactate it was always found to produce a sky-blue color. Milk infected 
with this organism was always found to be alkaline, but the blue color 
only appears when the milk turns sour, as the result of lactic-acid 
fermentation, or when acid is added to the milk. J. Reiset (29) ob- 
served that in dairies of some localities a blue mold forms on the 
surface of cow’s milk which has been allowed to stand. It has also 
been observed on the milk of ewes and goats. This mold was found to 
consist of mycelia containing immobile bacteria. The mold was 
found to grow only on milk having a distinctly acid reaction. 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 (30), 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 
