no 



BULLETIX 250. 



into the respiratory tract. It has recently been shown that tubercle bacilli 

 escape in large numbers with the intestinal discharges from many tuber- 

 culous cattle. They escape in the pus from tubercular abscesses that open 

 through the skin, and in the milk. It has been shown from all the exami- 

 nations that have been reported of milk from tuberculous cows, that 

 about fifteen per cent of them give ofif tubercle bacilli with their milk at 

 some time during the course of the disease. The udders show tubercu- 

 losis in about two per cent of the cases. 



2. The method of infection. 



Animals become infected with tubercle bacilli largely through the 

 digestive tract. The infection by means of inhaling particles of dirt or 



dust carrying tubercle bacilli, or 

 by getting them into wounds of 

 the skin, is possible but certainly 

 not very common. Healthy cat- 

 tle "nosing" with infected ones or 

 feeding and drinking after them 

 is the most usual method of con- 

 tracting the disease. Feeding 

 calves with milk from tubercu- 

 lous cows is a common means of 

 ])ropagating tuberculosis in a 

 herd. The slow development of 

 the disease makes it possible for 

 calves to be infected and fre- 

 quently not to show evidence of 

 tuberculosis for many years. I 

 have known of a very large 

 percentage of calves that were 

 fed upon milk of diseased cows 

 to give a good tuberculin re- 

 action (thus showing they were 

 suffering with active infections) 

 before they were six months old. 

 This is believed to be one of the very important ways by which the disease 

 is disseminated in breeding herds. 



Tuberculosis is often found in swine fed upon milk from infected cows. 

 In 1903 the writer knew of a carload of hogs that had been purchased in a 

 district where there were many tuberculous cows, and of which the first 

 fifty-nine of them that were slaughtered were all tuberculous. The 

 remainder were not killed at that time. While such a condition may 

 be considered an cxce])tir)n. it i^ a fact that many swine are infected, 



Fig. 129. — A dra-ivinf^ of the heart of a 

 steer that was killed for hccf. The heart 

 muscle is entirely surrounded by a dense 

 mass of tubercular deposit. There were 

 no other lesions found in the anunal. 



