156 AGRICULTURAL BACTERIOLOGY 



these abscesses are located in parts of the body from which 

 the bacilli may escape to the exterior on the breaking of. 

 the abscesses, the disease is said to be of the open type. 

 This stage in the progress of the disease is not reached for 

 a considerable number of months, or even years, after the 

 inception of the disease. Approximately 25 per cent, of 

 tubercular cattle have the open form of the disease. 

 The milk of such animals is likely to be contaminated with 

 the organism, the frequency and extent of the contamina- 

 tion depending upon the location of the abscesses. They 

 may be present in the udder, in which case the milk is 

 almost sure to be contaminated. If the abscesses are lo- 

 cated in the lungs, as is most commonly the case, the in- 

 fectious material will be coughed up from the lungs ; a por- 

 tion is ejected from the mouth, while the remainder is 

 swallowed. The tubercle bacilli therein are not destroyed 

 in their passage through the alimentary tract, and are 

 eliminated in the feces. Since some fecal matter inevitably 

 finds its way into milk, the opportunity is offered for con- 

 tamination of the milk with tubercle bacilli coming from 

 the lungs. Abscesses in the intestine or liver may serve to 

 contaminate the milk in the same manner. 



Tubercular abscesses in the udder may discharge their 

 contents directly into the milk-ducts. The extent of con- 

 tamination from the udder is much greater than from other 

 sources, and is probably of much greater importance: but 

 it is probably less frequent than contamination from the 

 lungs, either by means of the manure or the dust of the 

 stable. 



The percentage of milch-cows suffering from tuberculosis 

 varies widely in different parts of the world, but it is defi- 

 nitely appreciable in all sections where dairy development 

 has been considerable. It is probable that mixed milk sup- 



