322 APPLIED BACTERIOLOGY 



a boarding-school became consumptive subsequent to the 

 daily use of milk from a tuberculous cow. 



That the tubercle bacilli occurring in milk are virulent 

 has been proved by subjecting animals to subcutaneous 

 injection, and by feeding them with the infected milk. 



Dr. Martin writes* : ' The milk of cows with tuberculosis 

 of the udders possesses a virulence which can only be 

 described as extraordinary. All animals inoculated showed 

 tuberculosis in its most rapid form.' Dr. Woodhead, after 

 investigating the effects of unboiled tubercular milk, speaks 

 in similar terms of this virulence of milk derived from 

 tuberculous udders and inoculated into test animals. 

 These two observers had occasion to use milk from a cow 

 that had tuberculous disease in one quarter only of the 

 udder ; and they found the milk from the other three- 

 quarters to be perfectly harmless on inoculation ; but the 

 mixed milk from the four teats was to all appearance just 

 as virulent as the milk from the diseased quarter. Butter, 

 skimmed milk, butter-milk, obtained from the milk of a cow 

 having tuberculous udders, all contained tubercle bacilli. 



To some extent the chances of infection are reduced in 

 actual practice, as the milk as usually supplied to the 

 consumers is the mixed milk of a herd of cows, whereby a 

 tuberculous milk suffers considerable dilution with the milk 

 from healthy cows ; but this dilution, as shown by recent 

 experiments, only reduces the risk of infection, but does not 

 entirely do away with it. 



Freudenreich examined twenty-eight samples of mixed 

 milk, and found out of this number four that proved to 

 be virulent when inoculated into guinea-pigs. Two of 

 these samples came from dairies where from twenty to 

 thirty cows were kept, and where in each case only one 

 cow was suspected to be affected with tuberculosis. The 

 * Eoyal Commission on Tuberculosis (1895). 



