Infection of Milk. 67 



and the lesion is restricted in its development. Where 

 such a condition obtains, it is known as "closed," in 

 contradistinction to "open" tuberculosis, where the 

 diseased tissue is more or less broken down and is dis- 

 charging into the circulation, or elsewhere. Mani- 

 festly, the danger of spreading not only in the affected 

 animal itself, but to the outside, is much greater in the 

 case of the open lesion. Especially is this true where 

 the disease is present in the lungs or organs that have 

 an exterior opening so that the material containing 

 the organisms is discharged from the body in the 

 sputum, manure, urine or milk. The intestines them- 

 selves are rarely affected, but the lymph glands asso- 

 ciated with the intestinal tract are not infrequently in- 

 volved. 



Infection of milk with tubercle bacilli. In a small 

 percentage of cases, the udder itself becomes involved. 

 Where this condition obtains, one or more hard lumps 

 are formed, which slowly increase in size, usually being 

 restricted to one quarter of the udder. Sometimes the 

 affected quarter may develop to an enormous size, pro- 

 ducing a hard, painless tumor. Not often does the af- 

 fected tissue break down into pus ; consequently, no 

 abnormal appearance is to be noted in the milk secre- 

 tion until the disease has made very extended progress, 

 in which case the percentage of fat generally dimin- 

 ishes. Whenever the udder shows physical manifesta- 

 tion of this disease, the milk almost invariably is rich 

 in tubercle bacilli. 



Tubercle organisms may also appear in milk of ani- 

 mals in which no physical symptoms of the disease are 

 to be found. This fact has been demonstrated by micro- 



