DISEASES OF SWISE 479 



post-mortem inspection. This attack on the farmer's purse will 

 probably have more beneficial results in making him fully alive 

 to the seriousness of the situation than any other procedure. 



In an endeavor to trace the origin of the infection of tuber- 

 culosis hogs that were arriving at one of the packing plants of 

 Iowa, Rogers of the Bureau of Animal Industry for some time car- 

 ried on an experiment which consisted in tagging the hogs that 

 were hauled to market at that place in wagons, before they were 

 removed from the farmers' wagons, and later using these tags as 

 means of identification in case tuberculosis was found to exist in 

 any of the hogs at the time of slaughter. In this manner 3,420 

 hogs were tagged, and on tracing them to their final disposal it 

 was learned that all of the tuberculosis live stock brought to that 

 market came from a few farms less than 6 per cent of the total, 

 while the remaining 94 per cent of the farms were free from the 

 disease. This proportion of noninfected farms should give great 

 encouragement to any efforts that may be made to eradicate the 

 disease from the State. It was further noted that the successive 

 shipments of hogs marketed by certain farmers always contained 

 tuberculosis animals, and in at least two instances the entire con- 

 signments were condemned for tuberculosis at the time of slaugh- 

 ter. (B. A. I. Cir. 144.) 



Methods of Infection. As a result of numerous experiments 

 conducted on hogs it has been quite conclusively shown that hog 

 tuberculosis is an ingested disease and that the tubercle bacilli are 

 absorbed almost at the beginning of the alimentary canal. 



In a certain small number of cases infection probably occurs di- 

 rectly through the respiratory tract, but these instances are extremely 

 rare. Even more infrequent are those cases of tuberculosis which 

 arise 'as a result of traumatism, especially the infection of castra- 

 tion wounds by the use of infected instruments or otherwise. One 

 boar has come under our observation whose testicles and mucous 

 membrane of the penis were so markedly tuberculous that the geni- 

 tal tract of the sows covered by him could scarcely have escaped 

 infection. 



The most frequent infection of hogs with tuberculosis, as has 

 just been pointed out, occurs, no doubt, through the digestive tract, 

 and in this mode of infection tuberculosis of cattle is very inti- 

 mately concerned. In those instances in w r hich a marked increase 

 in the number of tuberculous hogs from a certain locality has been 

 noticed and investigated it has too frequently been found that the 

 hogs in question had been fed upon the by-products of a cream 

 separator or that the carcass of some animal succumbing to tuber- 

 culosis had been thrown to them for final disposal. The certainty 

 with which either of these two conditions will lead to the infection 

 of the hogs has not heretofore been appreciated in many quarters. 



Another source of infection for swine has been shown to exist 

 in the practice of allowing them to run behind a herd of cattle, 

 where the tubercle bacilli excreted with the feces by a tuberculous 

 bovine may readily infect the hogs. Infection of a litter of pigs 



