62 BOYIXE TrBERCTEOSIS AND OTHER CATTLE DISEASES. 



Contamination of milk by tubercle bacilli. The channels by 

 which tubercle bacilli are eliminated from the body of the 

 tubercular cow, have been carefully studied. The elimination 

 of tubercle bacilli from the mouth, in the saliva, is not of direct 

 importance in the contamination of milk. When the uterus 

 is involved, or the urine contains tubercle bacilli, the proba- 

 bility of the infection of the milk is great. The tubercular 

 udder, whether diseased so badly as to permit detection or 

 so slightly as to escape detection by physical examination, gives 

 off tubercle bacilli. In this connection, the conclusions of 

 Mohler (19) bearing on the point at issue, are quoted : 



"From the results of the experiments conducted in this Ia1x>ratory as 

 well as from the majority of similar investigations quoted in this article, 

 the following conclusions regarding the infectiousness of milk from tuber- 

 culous cows seem justifiable : 



"1. The tubercle bacillus may be demonstrated in milk from tuber- 

 culous cows when the udders show no perceptible evidence of the disease. 

 either macroscopically or microscopically. 



" 2. The bacillus of tuberculosis maybe excreted from such an udder 

 in sufficient numbers to produce infection in experimental animals both 

 by ingestion and inoculation. 



"3. That in cows suffering from tuberculosis the udder may, there- 

 fore, become infected at any moment.- 



' ' 4. The presence of the tubercle bacillus in the milk of tuberculous 

 COW T S is not constant, but varies from day to day. 



" 5. Cows secreting virulent milk may be affected with tuberculosis to 

 a degree that can be detected only by the tuberculin test. 



"6. The physical examination or general appearance of the cow can- 

 not foretell the infectiveness of the milk. 



"7. The milk of all cows which have reacted to the tuberculin test 

 should be considered as suspicious, and should be subjected to steriliz- 

 ation before using. 



"8. Still better, tuberculous cows should not be used for general dairv 

 purposes. ' ' 



I Ostertag (28) has reached contradictory conclusions, but in 

 view of all the facts available at present, the conditions encoun- 

 tered by him must be regarded as unusual. I /It has been shown 

 that an udder so slightly diseased as to Be detected only on 

 microscopic examination of the tissues, yielded tubercle bacilli 

 (29). The difficulty in determining exactly when an udder is 



