242 PATHOGENIC BACTERIA IN MILK 



dairy purposes.^ We know of no experiments on this subject which 

 have been so thorough as Dr Mohler's work, and we consider his 

 findings to be of great importance. Further, it should be re- 

 membered that his work does not stand alone, but is only con- 

 firmatory of many other similar experiments. Either the udder is 

 affected in a much larger proportion of cases than has been hitherto 

 admitted, or many cows with apparently sound udders excrete 

 tubercle bacilli in their milk. In any case, if these findings be 

 accepted, clinical examination of the udder cannot be admitted as 

 a reliable test of the presence or absence of tuberculous infectivity.^ 

 At the same time we must add that we believe the subject requires 

 careful and repeated experiment before absolutely final conclusions 

 can be drawn.^ 



The Virulence of Milk containing- Tubercle Bacilli 



In considering this question, it should be remembered that 

 " virulence " is only a relative term. There is no exact standard 

 of virulence. One strain of bacillus tuberculosis is highly virulent, 

 and a second strain the reverse. Hence it is only possible to deal 

 in a broad way with the virulence which milk may obtain from 

 tubercle bacilli. 



The virulence of milk from tuberculous udders was first insisted 

 upon by Klencke in 1846, and confirmed by Gerlach in 1869. Koch, 

 Bang, McFadyean, Woodhead, Hirschberger, Nocard, Crookshank, 

 and many others obtained evidence in support of the view which 

 is now universally accepted, namely, that milk drawn from a tuber- 

 culous udder is highly virulent to guinea-pigs and other animals. 

 Most observers go a step further, and assume that on this account 

 it is also virulent, in some measure, for man. 



* Bureau of Animal Industry^ Washington, Bulletin 44. " Infectiveness of 

 Milk of Cows which have reacted to the Tuberculin Test," John R. Mohler, 



1903. P- 93- 



2 See also Eighteenth Annual Report of Bureau of Animal Industry, Wash- 

 ington, 1 90 1, p. 263. 



^ Only recently Ostertag experimented on 10 cows which reacted to tuber- 

 culin and yet showed no signs of clinical tuberculosis. Inoculation of the milk 

 failed to set up any tuberculosis in guinea-pigs, and feeding calves and pigs with 

 the milk for many weeks also failed to set up disease. From these results it 

 was concluded that the milk of cows which simply reacted to tuberculin and had 

 no udder disease, does not contain tubercle bacilli (Exp. Sta. Rec, Oct. 1902) 

 J. H. Young of Aberdeen has also made some recent experiments on 14 cows 

 free from udder disease and yet reacting to tuberculin. Inoculations into 

 guinea-pigs proved negative {Brit. Med. Jour., 1903, i., p. 816). 



