188 FIRST PRINCIPLES OF AGRICULTURE. 



ducts, if clean and sweet, affect the quality of milk 

 only by virtue of the variations in their feeding value, 

 though the character of the products made from it may 

 be influenced to some extent. The feeding of cotton- 

 seed, for instance, has a tendency to increase the pro- 

 portion of solid fat, while gluten meal, on the other 

 hand, is said to increase the proportion of liquid fat. 



Useful Succulent Poods, as turnips, swedes, mangel- 

 wurzels, cabbage, etc., also affect the flavor of the milk; 

 and, in order to prevent as far as possible their unfa- 

 vorable effect, they should be fed immediately after 

 milking. Wet brewers' grains, distillery refuse, and en- 

 silage in an advanced state of fermentation, also exert 

 an unfavorable influence on the quality of the milk. 



Changes in Milk. It is well known that milk from 

 healthy cows, even under good practical conditions of 

 preservation, will remain sweet but a short time ; though, 

 if it could be drawn and placed so that no air could 

 come in contact with it, it would always remain sweet. 

 The changes in milk, or tendency to sour, are caused by 

 the entrance into it of ferments, or minute organisms 

 called " bacteria ; " and milk possesses in a marked de- 

 gree those properties which, given a suitable temperature, 

 favor their rapid development. 



Good and Bad Ferments. These bacteria are of 

 two classes, one of which includes those called " friendly," 

 which are necessary or helpful in the making of butter 

 or cheese, and the other, "unfriendly," or those which 

 introduce bad qualities into the milk and its products. 

 The ferments that injuriously affect milk are more abun- 

 dant in warm weather, in closed buildings, and around 



