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 ** 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 feces; the tubercle 
bacilli are not destroyed by the digestive secretions and 
remain virulent. Schroeder ** and the British tubercu- 
13 Joest and Kracht, Zeitschr. fiir Infectionskrank., etc., 
pp. 315-816, vol. 12, No. 4, 1912. 
14 Schroeder, p. 120, 25th Annual Report B. A. I. 
