Invasion of the Udder by Bacteria. 301 



and hermetically sealed in the bottles may remain sweet during an 

 ocean voyage to Europe and return. That milk, drawn with such 

 care, is not sterile, and that it ultimately teems with micro-organisms, 

 although sweet to the taste, is a fact which the writer has been 

 assured by unquestionable authority. Such behavior of milk might 

 be expected from the character of the micrococci isolated from the 

 udder, and is indicative of contamination from that source. 



Judged from the standpoint of the dairyman, who considers that 

 souring is the one and only harmful change in milk, the contamina- 

 tion of milk from the interior of the udder, so far as has been shown 

 in this work, might be disregarded as unimportant. Until more is 

 known of the ordinary and of the occasional bacterial inhabitants 

 of the udder and of tlieir ability to elaborate enzymes and toxic 

 substances, the writer urges the recognition of that source of the 

 contamination of milk. 



Conclusions. 



1. The lactiferous ducts of the nineteen udders examined harbor 

 bacteria throughout their whole extent. 



2. Our present knowledge concerning the place at which bacteria 

 first gain access to milk should be expressed somewhat as follows : 

 Milk, when secreted by the glands of the healthy udder, is sterile. 

 It may, however, immediately become contaminated by the bacteria 

 which are normally present in the smaller milk ducts of the 

 udder. 



3. The bacteria so far found in the interior of the udder appar- 

 ently do not affect milk seriously. This, however, does not preclude 

 the probability that forms more injurious to milk may invade the 

 udder. 



4. The constant contamination of milk from the udder suggests 

 an explanation for the frequent occurrence of certain " dairy bac- 

 teria" in milk. 



5. A study of the anatomy of the udder fails to disclose structu- 

 ral features which could prevent the invasion by bacteria. 



