L70 BACTERIA IN MILK 
growth of bacteria. B. prodigiosus, B. erythrogenes, and B. lacto 
rubifaciens are three species that have been described as having 
this power. None of them is of practical importance in the dairy. 
Red spots in cheeses do sometimes result from the growth of bac- 
teria, but red milk is the rarest ofoccurrences. Inaddition to these 
we sometimes hear of yellow milk, orange milk, green milk, 
amber-colored milk, and black milk. By carefully selecting the 
varieties of bacteria, and inoculating them into tubes of sterile 
milk there may be produced samples of milk, each showing differ- 
ent colors, all the colors of the rainbow being thus obtained. All 
of these phenomena do certainly occur in the bacteriological 
laboratory, and all are produced by the growth of different species 
of microédrganisms. But they are usually procured by inoculating 
sterile milk with particular kinds of bacteria and allowing them to 
act on the milk for many days. They are not ordinarily dairy 
phenomena, and will hardly ever be likely to appear as dairy in- 
fections. They are of scientific rather than of practical interest. 
Miscellaneous Faults.—There is a considerable list of troubles 
appearing occasionally in milk that are due to the growth of 
unusual bacteria. Some of these are the following: Premature 
curdling, the milk curdling too quickly and without souring; failure 
to curdle at all, even after several days; bad tastes such as turnip 
taste, rancid taste, putrid taste; difficulty im churning; bad tasting 
sour milk; yeasty smell; soapy consistency. These faults are all 
unusual and in all cases the growth of unusual bacteria is the 
cause. The remedy is always the same, more care in cleanliness 
and more thorough sterilization of the milk-vessels. Any sample 
of milk in which lactic acid bacteria fail to develop normally will 
be sure to show some trouble due to the growth of bacteria that 
happen to be present and whose rapid growth is not prevented by 
the acid-forming bacteria. Sometimes such troubles may be 
remedied by the addition to the milk of a culture of ordinary 
lactic acid bacteria. 
Alcoholic Fermentation of Milk.—Most sugar solutions will 
