CONTAMINATION OF MILK 59 



in the secreting portion of the gland and in the milk ducts 

 and cistern. The portals of entrance are two. When patho- 

 genic organisms are present in the circulating blood, they 

 may pass into the udder and possibly into the milk ducts 

 (foot-and-mouth disease). The more frequent manner is for 

 the organisms to lodge in 'the tissues of the udder, where 

 they grow, and from which they may be discharged into the 

 milk ducts by the breaking of the abscess (inflammation of 

 the udder, or tuberculosis). 



The second portal of entrance is through the exterior 

 openings of the teats. For a short time after milking the 

 end of the teat is moist, and in the case of animals that 

 leak the milk, constantly so. Bacteria collect at this point 

 and gain their way into the teat, milk cistern, and milk 

 ducts. Most of the forms that enter in this way do not 

 find favorable conditions for growth, and soon disappear. 

 Others are able to grow to some extent, and may penetrate 

 to the secreting tissues of the gland. As a rule, no patho- 

 logical disturbance follows the entrance of the bacteria, as 

 most are saprophytic forms. At times cases of udder inflam- 

 mation are produced by organisms entering through the teat. 

 Contagious garget is spread by the milker in this way. 



In order to determine the importance of this source of 

 bacteria, samples of milk should be collected in such a 

 manner as to exclude other sources of contamination. The 

 samples should be collected at different times during the 

 process of milking. The results obtained will give an idea 

 of the portion of the gland in which the largest number of 

 bacteria are found. If the first few streams drawn from a 

 quarter contain many more bacteria than the milk collected 

 at the end of the milking process, then it is evident that the 

 bacteria were largely in the teat and milk cistern. 



