SOURCES OF MILK BACTERIA. 139 
it has been removed from the stall, contains many thousands of 
bacteria. 
Since all the troublesome changes which occur in milk and 
make it such a difficult product to handle, are due to the action of 
bacteria upon the milk, it is to the interest of the dairyman, the milk 
distributor, and the consumer to have as few bacteria as possible. 
Therefore, it is a matter of much importance to learn the sources 
from which these milk bacteria are derived. Knowledge upon this 
point will enable the dairyman to adopt precautions in the produc- 
tion and caring for the milk that will materially reduce their number. 
A slight attention given at the right point will produce better results 
than a much greater attention unintelligently applied. 
The Cow. The first source of milk bacteria is the cow. Al- 
though the healthy cow secretes milk in a sterile condition, it is by no 
means sterile when it leaves the milk duct. There are always some 
bacteria in the ducts ready to be washed into the milking pail with the 
first jet of milk. At the close of the milking enough milk is left in 
the ducts to furnish food for bacteria, which may get in through the 
external opening; and between the milkings, at the warm tempera- 
ture of the cow's body, these bacteria multiply (Fig. 29). Bacteria 
are thus always abundant near the opening of the teat, although 
the inner parts of the duct contain smaller numbers. They are sure 
to contaminate the first jets of milk drawn, so that this first lot, 
called fore milk, always contains more bacteria than that drawn 
later in the milking. Toward the close of the milking the bacteria 
sometimes disappear, so that the last milk may be actually sterile 
when it leaves the duct. While this is not always the case, the last 
milk is always purer than the first. 
From these facts it follows that milk is sure to contain bacteria 
by the time it reaches the mouth of the milk duct. While, by the 
use of special precautions, small amounts of milk can be drawn so 
carefully as to avoid all bacteria, this is an impossible procedure in 
dairying, and the dairyman must recognize that there is no practical 
means by which he can obtain sterile miik. Indeed, it would avail 
but little if he could, for it would be contaminated almost at once 
from other sources. 
