DISEASES CAUSED BY INFECTED MILK 95 



How tubercle hacilli get into milk. Bovine tubercle 

 bacilli usually get into the milk in one of three ways : — 



(1) Directly: from a cow with tuberculosis of the udder, 

 in which case the milk contains large numbers of tubercle 

 bacilli as it flows from the teat. 



(2) Indirectly: from a cow having tuberculosis of the 

 lungs. In this case the tubercle bacilli are coughed up into 

 the mouth, swallowed by the cow, passed in the faeces, and 

 thus indirectly get into the milk. 



(3) The milk from healthy cows may contain tubercle 

 bacilli from admixture with other milk or from contamina- 

 tion with tuberculous material. ' 



Human tubercle bacilli occasionally get into the milk 

 from persons having pulmonary tuberculosis. Such persons 

 could contaminate the milk by coughing, sneezing, or 

 through infected hands, contaminated cloths, or unsanitary 

 actions. Hess actually found human tubercle bacilli in a 

 sample of New York market milk. 



In order for the bovine tubercle bacillus to contaminate 

 milk it is necessary that the tuberculosis in the cow should 

 be an open process; that is, the bacilli must be discharged 

 into the environment. The tubercle bacilli that are locked 

 up in a lymph gland, or in the nodules upon the peritoneum, 

 or in the bone or lung, or any other portion of the body, 

 do not endanger the milk supply. Experiments have shown 

 that it is more than probable that the healthy mammary 

 gland is an eflBcient filter so far as the tubercle bacillus is 

 concerned. Even when tubercle bacilh are in the blood 

 they probably do not pass through into the milk, unless the 

 udder is diseased. It is some comfort to know that in tuber- 

 culosis, the bacilli do not frequently invade the blood, and 

 that if they do so a healthy mammary gland may be de- 

 pended upon to filter them out. 



Of the various sources of tubercle bacilli in milk the most 

 serious is tuberculosis of the udder. This is for the reason 

 that incredibly large numbers of active virulent tubercle 



