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Abnormal fermentations of milk . — Under ordinary circumstances 
milk usually undergoes the lactic acid fermentation. It turns sour 
and curdles and the production of lactic acid puts a stop, tempora- 
rily at least, to all other bacterial changes. Hence in normal milk 
it is only rarely that fermentation other than souring occurs. Under 
certain conditions, however, the milk becomes infected with a great 
variety of micro-organisms and various changes in its composition 
are brought about. By some authorities these have been called 
abnormal fermentations. As a result of these fermentations, altera- 
tions take place in the color, odor, and taste of the milk, and in some 
instances highly poisonous substances are produced. In this con- 
nection Burri and Dueggeli (27) have recently had occasion to exam- 
ine four samples of milk in which such alterations had occurred. 
According to these authors sample (1) had the peculiarly disagree- 
able odor of Limburger cheese, sample (2) the odor of dogs, sample 
(3) a bitter taste, and sample (I) the odor and taste of Schabzieger 
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. AVhile 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 cleanl}^ 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 1811 
Fuchs (28) traced the production of blue milk to the growth of a 
micro-organism. By using Koch’s gelatin method Hueppe and Eng- 
ling (29) 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 in- 
fected with this organism was always found to be alkaline, but the 
blue color only appears when the milk turns sour, as the result of i 
lactic-acid fermentation, or when acid is added to the milk. J. Keiset 
(30) observed 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. 
