INFLUENCE OF DISEASE UPON MILK 83 



tunity to locate in the udder and to produce small, fresh 

 tubercles, too small to be discovered by palpation of the 

 udder. Such lesions may even escape observation on 

 post-mortem examination because of their similarity in 

 appearance to the actively secreting udder tissue. Rick 

 found the udder tuberculous in 17.6 per cent, of the cases 

 of generalized tuberculosis examined by him. Joest and 

 Kracht 13 found the supramammary lymph glands tuber- 

 culous, when tested by inoculation, in 50 per cent, of the 

 cases examined by them of generalized tuberculosis in 

 which the udder did not show any clinical symptoms or 

 macroscopic lesions on post-mortem examination; some 

 of the lymph glands were slightly enlarged but otherwise 

 they were of normal appearance. In one-half of these 

 cases the udder tissue was also infected. It would there- 

 fore appear that the udder is much more frequently tuber- 

 culous in cases of generalized tuberculosis than is gener- 

 ally suspected. 



Contradictory views exist as to the possibility of 

 tubercle bacilli passing through the sound udder. Oster- 

 tag and Prettner injected tubercle bacilli intravenously 

 into cows with sound udders and found the milk non- 

 virulent when inoculated into guinea pigs. 



Milk may be infected secondarily with tubercle bacilli 

 when open tuberculosis is present in the lungs, intestines, 

 or uterus. Cows affected with open tuberculosis of the 

 lungs swallow the greater part of the infected material 

 coughed up, and it passes out with the fasces; the tubercle 

 bacilli are not destroyed by the digestive secretions and 

 remain virulent. Schroeder 14 and the British tubercu- 



13 Joest and Kracht, Zeitschr. fur Infectionskrank., etc., 

 pp. 315-316, vol. 12, No. 4, 1912. 



14 Schroeder, p. 120, 25th Annual Report B. A. I. 



