MILK-BORNE TUBERCULOSIS 203 



milk affords an ideal medium for bacteria, and its adaptability there- 

 fore for conveying pathogenic organisms is undoubted. We shall 

 speak shortly of the outstanding facts of the chief diseases carried by 

 milk. 



Milk-bopne Tuberculosis 



It is a well-known fact that tuberculosis is a common disease of 

 cattle. Probably not less than 20 to 30 per cent, of milch cows in 

 this country are affected with it. Therefore, at first sight it might 

 appear that the consumption of milk from such animals would lead 

 to considerable spread of the disease. But in point of fact there are 

 two limiting conditions. The first has relation to the question of 

 the communicability of the disease from the cow to man. The 

 second concerns the degree of disease in the cow which can affect the 

 milk. It is necessary that both points should be discussed some- 

 what fully. But the former question will be discussed in the chapter 

 dealing with Tuberculosis (see pp. 338-346). The latter condition 

 only will be discussed here. It has reference to that which limits the 

 transmissibility of tuberculosis from the cow to man by means of 

 milk has relation to the well-established fact that the milk of tuber- 

 culous cows is only certainly infective when the tuberculous disease 

 affects the udder* This is not necessarily a condition of advanced 

 tuberculosis. The udder may become infected at a comparatively early 

 stage. The presence or absence of tubercle bacilli in the milk of cows 



* This is the generally accepted view, but it should be added that various 

 workers have shown that cows having generalised tuberculosis, but apparently un- 

 affected udders, may yield tuberculous milk. Quite recently (1903) Mohler, as the 

 result of a long series of experiments, arrives at the following important con- 

 clusions : — (1) That the tubercle bacillus may be demonstrated in milk from tuber- 

 culous cows when the udders show no perceptible evidence of disease either 

 macroscopically or microscopically ; (2) that the bacillus of tuberculosis may be 

 excreted from such an udder in sufBcient numbers to produce infection in experi- 

 mental animals, both by ingestion and inoculation ; (3) that in cows suffering from 

 tuberculosis the udder may, therefore, become affected at any moment ; (4) that the 

 presence of the tubercle bacillus in the milk of tuberculous cows is not constant, but 

 varies from day to day ; (5) that cows secreting virulent milk may be affected with 

 tuberculosis to a degree that can be detected only by the tuberculin test; (6) that 

 the physical examination or general appearance of the animal cannot foretell the 

 infectiveness of the milk ; (7) that the milk of all cows which have reacted to the 

 tubercuUn test should be considered as suspicious, and should be subjected to 

 sterilisation before using ; and (8) that it would be better still that tuberculous cows 

 should not be used for general dairy purposes.* Experiments by Lydia Rabino- 

 witsch have given somewhat similar results. She relies on tuberculin as a test of 

 infectivity, and the animal experiment as proof of tuberculosis in mUk. f Ravenel 

 also maintains that cows which show no evidence of tuberculous udders, but which 

 react to tuberculin, may yield tubercle bacilli in their milk. J. H. Young of Aberdeen 

 maintains, on the other hand, that cows free from udder disease though reacting to 

 tuberculin yield milk free from tuberculosis. J 



* Bureau of Animal Industry, Washington, U.S.A., Bulletin 44, 1903, p. 93. 

 t See also Zeitschrift fiir Thiermedicin, 1904, p. 202, 

 $ Brit. Med. Jovr., 1903, i., p. 816, 



