TYPES OF BACTERIA FOUND IN MILK. 157 
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 different 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 microorganisms. 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 ap- 
pear as dairy infections. 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 in 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 al- 
ways the same, more care in cleanliness and more thorough steriliza- 
tion 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-foiming bacteria. Some- 
times 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 
readily undergo an alcoholic fermentation, but milk sugar does not 
easily make this change. It may be converted into lactic acid, 
but not readily into carbon dioxid and alcohol. Hence an alcoholic 
fermentation of milk is not a normal phenomenon, although it may 
be pioduced by the addition of a little cane-sugar to the milk. The 
possibility of making milk undergo an alcoholic fermentation by the 
addition of yeasts is made use of in the manufacture of kummys. 
This beverage was originally prepared by the Arabs from mare's 
milk, which will normally undergo an alcoholic fermentation; but 
