86 Dairy Bacteriology. 



especially between the ages of two and five. 1 It is difficult 

 to determine, though, whether primary infection occurred 

 through the intestine, for, usually, other organs also be- 

 come involved. In a considerable number of cases in which 

 tubercular infection by the most common channel, inhala- 

 tion, seems to be excluded, the evidence is strong that the 

 disease was contracted through the medium of the milk, but 

 it is always very difficult to exclude the possibility of pul- 

 monary infection. 



Tuberculosis as a bovine disease has increased rapidly 

 during recent decades throughout many portions of the 

 world. This has been most marked in dairy regions. Its 

 extremely insidious nature does not permit of an early rec- 

 ognition by physical means, and it was not until the intro- 

 duction of the tuberculin test * in 1892, as a diagnostic aid 

 that accurate knowledge of its distribution was possible. 

 The quite general introduction of this test in many regions 

 has revealed an alarmingly large percentage of animals as 

 affected. In Denmark in 1894 over forty per cent were 

 diagnosed as tubercular. In some parts of Germany almost 

 as bad a condition has been revealed. Slaughter-house sta- 

 tistics also show that the disease has increased rapidly since 

 1890. In this country the disease on the average is much 

 less than in Europe and is also very irregularly distributed. 

 In herds where it gained a foothold some years aO, often 

 the majority of animals are frequently infected; many 



' Stille, Brit. Med. Journ., Aug. 19, 1899. 



2 This test is made by injecting into the animal a small quantity of tuberculin, 

 which is a sterilized glycerin extract of cultures of the tubercle bacillus. In a 

 tuberculous animal, even in the very earliest phases of the disease, tuberculin 

 causes a temporary fever that lasts for a few hours. By taking the temperature 

 a number of times before and after injection it is possible to readily recognize 

 any febrile condition. A positive diagnosis is made where the temperature after 

 inoculation is at least 2.0 F. above the average normal, and where the reaction 

 fever is continued for a period of some hours. 



