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- 

 lure 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. 



