138 



AGRICULTURAL BACTERIOLOGY 



drawn from the animal it comes in contact with the bacteria 

 that have invaded the udder through the opening of the 

 teat and have established themselves throughout the 



spaces or channels which ramify 

 through this organ. The greater 

 number of organisms are found 

 in the lower portion of the ud- 

 der, in the milk cistern and in 

 the large milk ducts. The open- 

 ing of the teat comes in contact 

 with material that contains the 

 most varied kinds of bacteria, 

 and it is probable that the milk 

 ducts are invaded by many 

 kinds. Only certain types, how- 

 ever, are able to grow in the ud- 

 der, and these only to a limited 

 extent. As will be seen later, all 

 body fluids have a germicidal ac- 

 tion. The germicidal action of 

 milk probably explains why the 

 growth of the bacteria that in- 

 vade the udder is not nearly so 

 rapid as one would expect under 

 the favorable conditions with 

 reference to food and tempera- 

 ture. It has been shown that no 

 bacterial increase occurs in milk for a period after it is 

 drawn. This has usually been ascribed to the germicidal 

 action of the milk. Whatever action milk may exhibit in 

 this direction, it is of small importance in the practical 

 handling of the product. 



The kinds of bacteria that are able to grow in the udder 

 are not those that are actively concerned in the spoiling 



29. A Section of an 

 Udder 



The milk is conducted from the 

 secreting colls by the milk ducts 

 which empty into the milk cis- 

 tern from which it is drawn 

 through the teats. Bacteria en- 

 ter the teats and penetrate into 

 the smallest of the milk ducts 



