144 APPLIED BACTERIOLOGY 



five out of fourteen young girls living together in a board- 

 ing 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 

 * Royal Commission on Tuberculosis (1895). 



