SOURCES OF DANGER IN MILK 315 
sterile, but it is a much safer food, especially for infants. 
At best pasteurization is only a corrective or precautionary 
measure, and we should demand that milk be kept clean and 
thus free from bacteria. 
Most raw milk products have their own forms of bacteria, 
nearly all of which are helpful. The flavor of June butter is 
imparted by a bacterium different from the one in January 
butter. So with cheese, each brand or flavor receives its 
taste through the action 
of a special bacterium. 
At every step in the use 
and manufacture of milk, 
it is necessary to know 
the conditions under 
which the helpful bac¬ 
teria work best, and how 
to keep out the harmful 
ones. 
270. Sources of Dan¬ 
ger in Milk. — The cow 
herself may be unhealthy 
and her disease trans¬ 
mitted through the milk. 
Of the several diseases 
which this animal may 
give, tuberculosis is the 
most common. Children are more liable than adults to 
take the disease in this way. There is no necessity to be 
in doubt about a cow’s being infected with tuberculosis, 
for in 1890 Koch discovered the tuberculin test, which 
enables the dairyman to detect the disease. This test is 
now commonly applied, and in some cities owners of herds 
which have been tested and found free from disease are 
allowed to sell their milk as “ certified,” though the mean¬ 
ing of this term varies. Not only is the raw milk from 
Figure 289. 
The metal cap keeps out dirt which can 
get by the paper stopper. 
