60 BOVINE TUBERCULOSIS AND OTHER CATTLE DISEASES. 



ticable scheme yet devised for the control of tuberculosis, 

 the Bang method (21, 22, 23, 34, 35, 36, 38, 39, 54). 



Infection of swine. (^But the tubercular cow is not merely a 

 menace to her young through the milk, but also casts a blight 

 upon the industry of pork production. The pig is particularly 

 susceptible to bovine tuberculosis. In districts where it is the 

 common practice to feed pigs on skim-milk and whey, the 

 results occasion the condemnation of such a high per cent, of 

 carcasses that buyers have learned to avoid certain districts on 

 this account. In any event, they pay a price for pork lowered 

 in anticipation of their losses from condemned carcasses or 

 parts. 



Milk is not the only common means for the transmission of 

 tuberculosis by cattle.,, In the corn belt, pigs are raised in 

 association with beef cattle, so that they may utilize the feces 

 of cattle for feed. The magnitude of the losses occasioned in 

 this way has drawn attention to the matter of contamination 

 by feces as a source of the tubercle bacilli in milk (41, 42, 45). 



Insidious onset. The insidious nature of the disease masks 

 its presence and wholly misleads the dairymen as to the 

 number of his cattle that are tubercular. A cow may be in 

 fine condition and apparently perfect health, and on slaughter 

 show the most serious advanced stage of involvement of the 

 internal organs. This is so common that the diagnosis by 

 physical examination by a veterinarian is entirely unsatisfactory. 



Conditions governing prevalence . The prevalence of tubercu- 

 losis in herds seems to depend to a large extent upon the 

 number of opportunities that have been offered for the possible 

 introduction of infection. Small herds which have been built 

 up of calves raised on their mothers' milk, will be found in the 

 best condition (55). The large herds supplying city milk are 

 conducted upon a different plan, Dry cows are frequently 

 i* sold, and their place taken by cows which have been bought 

 shortly before calving. Calves are butchered, for whole milk 

 is too precious to feed them and no skim-milk is available. 

 Under these conditions, there is every opportunity offered for 

 the introduction of tuberculosis. Among the dairies in which 

 calves are raised on skim-milk, a different source of infection 



