276 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



Investigations have been made to determine how much danger 

 there is from the exposure of healthy to tuberculous hogs. These 

 investigations are not yet complete, but as far as they have gone it is 

 seemingly fair to conclude that contact of healthy with tuberculous 

 hogs in a hog yard is not nearly the dangerous source of infection 

 that the exposure of hogs to tuberculous cattle or to the feces of 

 tuberculous cattle has been proven to be. 



Some time ago the station proved that the commonest way for 

 tuberculous cattle to expel tubercle bacilli is with their feces through 

 their bowels. It was found that hogs exposed to the fresh manure of 

 a herd of tuberculous cattle very rapidly became tuberculous. In 

 this connection it seemed desirable to gain some information about the 

 length of time that tubercle bacilli will remain alive and virulent in 

 cattle feces, and especially in manure piles. Experiments made rela- 

 tive to this matter showed that tubercle bacilli die very rapidly on the 

 exposed surface of manure, but that in the depth of a manure pile 

 they may remain sufficiently virulent for months to cause tubercu- 

 losis in hogs that are exposed to the pile after a layer less than a foot 

 thick has been removed from its surface. Hence, as in all the other 

 work done by the station on the vitality and virulence of tubercle 

 bacilli, the fact is here again illustrated that the bacterium of tubercu- 

 losis has an enormous amount of resistance to adverse conditions, 

 provided it is not exposed to light or to a temperature which is high 

 enough for the pasteurization of milk. This investigation is not yet 

 fully completed, but we can now say with certainty that tubercle 

 bacilli, capable of causing tuberculosis in hogs, may live more than 

 three months in a manure pile from a stable of tuberculous cattle. 



Some work done in connection with the pasteurization of milk, in 

 which the milk was obtained from a cow affected with udder tuber- 

 culosis, showed that a temperature of (')0° C. (140° F.), maintained for 

 twenty minutes, invariably killed the tubercle bacilli. Over 100 

 guinea pigs injected with such pasteurized milk remained free from 

 tuberculosis, while an equal number injected with unpasteurized milk 

 from the same source contracted generalized tuberculosis with very few 

 exceptions. 



An experiment is still in progress relative to the elimination of 

 tuberculosis from a herd of tuberculous cattle, and the derivation, in 

 the most economical way, of a herd of sound cattle from one that is 

 affected with this disease. It will be some time, however, before a 

 report on this work can be written. At present we can say that con- 

 genital tuberculosis among calves is very rare unless they are pro- 

 duced by cows affected with very advanced tuberculosis, and that 

 calves rarel^'^ contract tuberculosis during the first few weeks of their 

 lives from exposure to their dams when the latter are not clinically 

 affected and have sound udders. Milk from a tuberculous udder 

 means the rapid and practically certain infection of all cah^es that 

 drink it. 



Among a number of tuberculous cattle kept for a long time at the 

 station one observation is of considerable practical importance. It 

 seems that when tuberculous cows are kept any length of time after 

 the disease is somewhat advanced or has become clinically determin- 

 able, the development of udder tuberculosis and the extreme infection 

 of the milk with tubercle bacilli is very common. 



