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chief seats of tuberculosis, it is evident that infection oc- 

 curred bj way of the alimentary canal. Occasionally the 

 family milch cow becomes tuberculous by eating the waste 

 slops and other materials which come from the house or rooms 

 where tuberculous persons live. The alimentary canal may 

 become the secondary seat of the disease by the animal or 

 person coughing up the infectious material from the lungs 

 to the pharynx or mouth and then swallowing it. 



(3). Infection by direct inoculation. — If a terbuculous 

 animal drops infected sputa or saliva upon a freshly abraded 

 surface of a healthy animal infection might occur. Or a 

 diseased animal might lick the freshly abraded surface of 

 another and thus infection could take place. However, in- 

 fection b}^ this method is extremely rare. 



(4). Intra-Ulterine Infection. — The bacilli may pass by 

 way of the uterus and foetal membranes, or by way of the 

 blood vessels, from the mother to the foetus. The foetus or 

 unborn embryo, by tuberculous semen from the sire, or a 

 tuberculous ovum from the dam, may become infected. Re- 

 corded cases of infection by this method are extremely 

 rare. 



(5). It is also asserted that when the genital organs of 

 either sire or dam are infected, the tuberculous one may 

 transmit the bacilli to the other during copulation. 



THE ACTION OF TUBERCLE BACILLI IN THE TISSUES. 



After the bacilli gain admission (by any method of infec- 

 tion) to the tissues, they multiply at the point of lodgement 

 and there produce the tubercle. A young tubercle is com- 

 posed of a collection of cells forming a small grayish nodule 

 and the fresh state presenting the appearance of mother of 

 pearl. Two or more tubercles lying near one another in 

 the lungs, liver, spleen or kidney may unite or become con- 

 fluent as they continue to develop. Later in the development 

 of the tubercle the central mass becomes "cbeesy" — formino- 

 a large, soft, yellow, pus-like mass that is sometimes called a 



yellow tubercle. The growth of the tubercle advances by 

 2 



