BACILLUS TUBERCULOSIS AND ALLIED ORGANISMS 1 19 



ance, are constantly exposed to the infection through inhal- 

 ation, and to intestinal infection through milk and other foods. 



Immunity. No one can be said to be immune, though per- 

 sons who have been greatly weakened offer less resistance 

 than healthy individuals. 



Bovine and Human Tuberculosis. Tuberculosis in 

 Animals. Tuberculosis is probably the most widely dis- 

 seminated disease among domestic animals, and affects 

 cattle, pigs, horses, dogs, cats, the smaller ruminants, birds, 

 and even turtles and fish. The conclusion of Koch, made 

 public in his address to the Tuberculosis Congress in 1901, 

 that human and bovine tuberculosis are distinct and that in- 

 fection of human beings from cattle occurs so seldom that no 

 general regulations to restrict it are necessary, has found 

 few adherents. In 1908 Koch reiterated his idea and chal- 

 lenged his opponents to bring proofs to the contrary. Con- 

 clusions at this writing seem to be that go per cent, of all 

 pulmonary cases in adult man are not due to bovine infection. 

 In children under five, however, 10 per cent, of the intestinal 

 tuberculosis and cervical adenitis are due to the bovine 

 type of infection through milk of diseased cows. It is true 

 that certain differences exist between human and bovine 

 tubercle bacilli, the latter appearing to be more virulent to 

 animals, and it is a fact that cattle are very slightly suscepti- 

 ble to the human bacillus, but it is not likely that the con- 

 verse is so. Children are particularly liable to infection 

 through the gastro-intestinai tract, and it has been shown 

 that the uninjured mucosa of the infant's intestine is per- 

 meable to bacilli, so that the pulmonary disease in the 

 young may often be the result of tuberculous bronchial nodes 

 secondary to tuberculous glands of the mesentery. 



Various observations on animals have shown that the 

 bacillus occurring in each species has acquired certain special 

 characteristics regarding growth and virulence. The bacilli 

 causing tuberculosis in the cold-blooded animals have de- 

 parted farthest from the human type, those of birds to a less 

 degree, and those of cattle least of all. 



